forces by qingyunliuliu

VIEWS: 20 PAGES: 87

									     FORCES AND THEIR
     EFFECTS
                            Unit 7K
                         Year 7 Science


Saturday, 23 July 2011                    1
     Index
    introduction
    lesson 1: Are some magnets stronger than others?
    lesson 2: What forces act on a parachute?
    Homework task 2
    lesson 3: How much do balls bounce?
    lesson 4: Do rollers make it easier to drag heavy things?
    lesson 5: Why is iron heavier than aluminium?
    lesson 6: Are objects lighter under water?
    lesson 7: Why are some toy cars faster than others?
    lesson 8: Do things float better in salty water?
    lesson 9: Is friction sometimes useful?
    lesson 10: Do pulleys help with lifting?

Saturday, 23 July 2011                                          3
     Forces
     • What are forces?
     • How do we measure forces?
     • How do we use forces in our ordinary
       lives?
     • How do forces affect our lives?



Saturday, 23 July 2011                        4
     What do all these terms mean?
     • FORCE: the influence that produces a
       change in a physical quantity; "force equals
       mass times acceleration" (Newtons)
     • POWER: the rate of doing work; measured in
       watts (joules per second)
     • WORK: "work equals force times distance"
     • ENERGY: the capacity of a physical system
       to do work (joules)

Saturday, 23 July 2011                                5
Introduction
     Getting help
              You will be loaned a study guide

              Use our web site


     This unit is all about FORCES
     pushes, pulls and twists
     Forces are measured in NEWTONS

       http://www.westwightmiddle.iow.sch.uk/science.htm
Saturday, 23 July 2011                                     6
     Lesson 1

               Are some magnets stronger than
                         others?



Saturday, 23 July 2011                          7
     Objectives
     and what I am looking for
• Learn about             • Learn how to use
  magnetic force            the guide mats
• Learn to list the key   • Make a proper
  variables effectively     variables list
• Learn to evaluate       • Record your results
  the way you work          in a table
• Make careful
  measurements.
Saturday, 23 July 2011                      8
     Equipment
     •   A variety of different magnets
     •   30 cm rules marked in mm
     •   Steel ball bearings
     •   Results tables
     •   Level mats
     •   Study guides (3 levels differentiated)



Saturday, 23 July 2011                            9
Are some magnets              Learn to list the key
                              variables effectively
stronger than others?         Learn to evaluate the
                              way you work
                              Make careful
                              measurements.




                        • Watch a demonstration
                        of how to test.
                        • What are variables?
                        • Use whiteboards to list
                        the variables.

Saturday, 23
July 2011                                       10
Are some magnets                          Learn to list the key
                                          variables effectively
stronger than others?                     Learn to evaluate the
                                          way you work
                                          Make careful
New page. Date and title in your book.    measurements.


       Planning

       1. Make a list of the key
          variables
       2. Which variable will you test?
       3. Which variable will you
          measure?
       4. Which variables will you keep
          the same?
Saturday, 23 July 2011                                      11
                               Learn to list the key
Are some magnets               variables effectively
stronger than others?          Learn to evaluate the
                               way you work
                               Make careful
                               measurements.


 • Put the ball bearing on the table.
 • Move the magnet nearer to the ball bearing.
 • How close was the magnet when the ball
   started to move? Measure.
 • Record your results and try again with a
   different magnet.

Saturday, 23 July 2011                           12
                                                      Learn to list the key
Are some magnets stronger                             variables effectively
than others?                                          Learn to evaluate the
                                                      way you work
                                                      Make careful
                                                      measurements.
Let’s share our results
       Magnet             How close was the magnet?




                                                         Observations
                                                         State which
                                                         magnet is the
                                                         strongest
                                                         according to
                                                         your results.

Saturday, 23 July 2011                                                  13
                                         Learn to list the key
Are some magnets                         variables effectively
stronger than others?                    Learn to evaluate the
                                         way you work
                                         Make careful
                                         measurements.

                         Work in pairs
     Evaluation
     • How well did your test go?
     • Did you feel that your results were accurate?
     • How could you have improved your test in
       order to get more accurate results or results
       you could have been more sure of?


Saturday, 23 July 2011                                     14
     Lesson 2

               What forces act on a parachute?




Saturday, 23 July 2011                           15
     What forces act on a parachute?

      Parachute video (it might work)




Saturday, 23 July 2011                  16
     Equipment
     •   Digital camera
     •   A football
     •   Parachutes
     •   Timers
     •   Whiteboards, pens & erasers
     •   Study guides (3 levels differentiated)

Saturday, 23 July 2011                            17
     OBJECTIVES
     & what I am looking for
     • To learn about a    • Make a diagram that
       force called DRAG     clearly shows the
     • To learn to draw      forces that act on it.
       force diagrams      • Write to describe
                             which force is
     • To learn how to       largest.
       mark forces on a
                           • Write to explain how
       diagram               you know.

Saturday, 23 July 2011                           18
How to mark force                 To learn about a
                                  force called DRAG

arrows on diagrams.               To learn to draw
                                  force diagrams
                                  To learn how to
                                  mark forces on a
                         lift     diagram




                                       drag

               thrust
                                  New page, date
                                  & title.
                         weight
                                  Copy the
                                  diagram.
Saturday, 23 July 2011                        19
                                             To learn about a
Football                                     force called DRAG
                                             To learn to draw
                                             force diagrams
                                             To learn how to
                                             mark forces on a
                                             diagram


                         • We will go into the
                           playground to watch a
                           football and bring back a
                           photograph.



Saturday, 23 July 2011                                     20
Football photograph


    • Trim and fix the photograph into your
      book.
    • Use arrows and straight lines to mark:
         – Gravity
                                     To learn about a
         – Drag                      force called DRAG
                                     To learn to draw
                                     force diagrams
                                     To learn how to
                                     mark forces on a
Saturday, 23 July 2011               diagram       21
     Next bit…
     • DVD video input: BBC Class clips




Saturday, 23 July 2011                    22
Plenary: What                                    To learn about a
                                                 force called DRAG

forces act on a                                  To learn to draw
                                                 force diagrams

parachute?                                       To learn how to
                                                 mark forces on a
                                                 diagram



       Work in pairs
                                                       HOMEWORK

•   Try a parachute in the lab from a height of exactly 2 metres.
•   NOW RECORD THIS ON YOUR GROUP’S WHITEBOARD
•   Decide what force pulls the parachute down.
•   Decide what force holds the parachute up.
•   Which of the forces was greatest? Explain how you know.

Saturday, 23 July 2011                                       23
What forces act on                      To learn about a
                                        force called DRAG

a parachute?                            To learn to draw
                                        force diagrams
                                        To learn how to
                                        mark forces on a
   IN YOUR BOOK                         diagram

     • The force that pulls the parachute down is…
     • The force that holds the parachute up is.
     • Draw an accurate 2d diagram that shows the
       parachute and the two forces acting on it.
     • The force that was greatest was… I know
       this because…


Saturday, 23 July 2011                              24
     Finishing up
     • Forces ‘Hammer & Feather on the
       Moon’. (Class Clips DVD)




Saturday, 23 July 2011                   25
     Homework task 2
     • Use your knowledge of DRAG to
       explain why sports cars are streamlined.




HOMEWOK SHEET

Saturday, 23 July 2011                       26
Use your knowledge of DRAG                Use your knowledge of DRAG
to explain why sports cars are            to explain why sports cars are
streamlined.                              streamlined.
Use your knowledge of DRAG                Use your knowledge of DRAG
to explain why sports cars are            to explain why sports cars are
streamlined.                              streamlined.
Use your knowledge of DRAG                Use your knowledge of DRAG
to explain why sports cars are            to explain why sports cars are
streamlined.                              streamlined.
Use your knowledge of DRAG                Use your knowledge of DRAG
to explain why sports cars are            to explain why sports cars are
streamlined.                              streamlined.
                          Use your knowledge of DRAG
                          to explain why sports cars are
 Saturday, 23 July 2011   streamlined.                            27
     Lesson 3

                    How much do balls bounce?




Saturday, 23 July 2011                          28
     Getting started…

     • Draw a ball falling. Think about its
       shape.
     • Draw a ball that has hit the ground and
       is about to bounce back up. Think about
       its shape.


Saturday, 23 July 2011                       29
     OBJECTIVES
     & what I am looking for
   • How do forces make        • Be able to do a test and
     things bounce?              make accurate
   • Are my measurements         measurements.
     accurate?                 • Be able to repeat
                                 measurements to check.
   • Why is it important to
     repeat my tests?          • Be able to clearly describe
                                 what happened.
   • How can I use my
                               • Be able to use your
     scientific knowledge to
                                 knowledge to explain how
     explain?                    and why things happen.


Saturday, 23 July 2011                                    30
     Which forces make balls
     bounce?

                           1st
                         bounce



                                   2nd
                                  bounce




Saturday, 23 July 2011                     31
                            Equipment



     Equipment
     • Clamp stand with
                                            table tennis ball
       clamp and boss.
     • Metre rule.            clamp stand
     • Table tennis ball.
     • Results table.          metre
                               rule
     • Study guides.



Saturday, 23 July 2011                                    32
Results
                         test number   first bounce   second bounce


                             1


                             2


                             3


                             4


                             5


                             6


                             7


                             8


                             9


                             10




Saturday, 23 July 2011                                                33
     Conclusion
     • According to your results, describe what
       happened.
     • Use your understanding to explain why
       the first bounce was more than the
       second bounce.



Saturday, 23 July 2011                        34
     Something to think about…
     • The falling ball had kinetic energy
       because it was moving.
     • The amount of movement got less after
       the first bounce.
     • So, where did the kinetic energy go?



Saturday, 23 July 2011                     35
     Plenary & finishing off…
     • Your group might be asked to read your
       conclusion.
     • Copy your conclusion to your exercise
       book. Improve it as you go.
     • Homework: Complete the conclusion in
       your book.


Saturday, 23 July 2011                      36
 Forces & their effects: Lesson 4

                Do rollers make it easier to drag
                         heavy things?



Saturday, 23 July 2011                              37
     Just for starters…
     • Draw a picture of a bloke dragging a
       heavy rock.
     • Draw a picture of the same bloke
       dragging a heavy rock using rollers.



      •Can you show which one is the hardest
      work?
Saturday, 23 July 2011                         38
     OBJECTIVES
     & what I am looking for
     • To learn how to          • Know about control,
       write why your test        independent and
                                  dependent variables.
       is fair.
                                • Write a useful
     • To learn how to            prediction.
       make a useful bar        • Record your results
       chart.                     accurately.
     • To extend your           • Write to explain why
       ability to explain why     things happened.
       things happen.           • Write an evaluation.
Saturday, 23 July 2011                                   39
     Equipment



                         FOR GROUP WORK:
                         • Dowel rollers
                         • Force meters
                         • String
                         • A brick
                         • Study guiders
                         • Results tables
                         • Level mats




Saturday, 23 July 2011               40
     Key variables
     INDEPENDENT VARIABLE
       The variable I will test is…
     DEPENDENT VARIABLE
       The variable I will measure is…
     CONTROL VARIABLES
       The variables I will keep the same are…
                         Redraft into your exercise book.
Saturday, 23 July 2011                                      41
     Practical bit…

                         RESULTS
                            Test number   How much force     How much force
                                          without rollers?    with rollers?
   Use a board                  1
   to protect                   2
   your bench.                  3

                                4

                                5




Saturday, 23 July 2011                                                  42
     Conclusion


     • Produce a graph that shows these
       results clearly. [What should my graph
       look like?]
     • Write to explain what happened in terms
       of forces and energy. [What should my
       work look like?]
     • Plenary: Evaluate your test.
Saturday, 23 July 2011                      43
    A clear graph
                         16
                         14
                         12
                                                               1
                         10
                                                               2
             Force (N)




                          8
                                                               3
                          6
                                                               4
                          4
                                                               5
                          2
                          0
                              Without rollers   With rollers


                     CONCLUSION
Saturday, 23 July 2011                 PAGE                        44
    Model conclusion
        If the brick is dragged along the ground, the rough
        surfaces lock together and make lots of friction.
        All of the surface of the brick is touching the ground.
        The bigger the surface, the more friction there is.
        It takes a lot of force to drag the brick.


        If you use rollers, the rough surfaces do not lock
        together and so there is much less friction. So it takes
        much less force to pull the block.

Saturday, 23 July 2011 PREVIOUS PAGE                              45
     Forces & their effects:
     Lesson 5
                         Why is iron heavier than
                               aluminium?



Saturday, 23 July 2011                              46
      OBJECTIVES
      & what I am looking for
     • To learn the idea of   • You can measure
       density.                 mass in grams.
     • To learn to measure    • You can measure
       and compare              volume in cm³ .
       different materials.   • You can record your
                                results in tables.
                              • You can calculate
                                the mass of 1 cm³ of
                                each material.

Saturday, 23 July 2011                             47
     Equipment
     FOR GROUP USE
     • Metal blocks (materials kit) Iron, brass,
       aluminium & lead HAZARD
     • Electronic scales
     • Study guides



Saturday, 23 July 2011                             48
     Stage 1
    • What is the mass of each metal block?
      (Measure in grams)
    • Make a table of your results.
                            metal      mass g
                             iron
                            brass
                           aluminium
                             lead
Saturday, 23 July 2011                          49
     Was this a fair comparison?
                             brass

                  iron               lead




                         aluminium




            • Describe why your test is not fair.
            • Can you work out what the mass
              would be if every block was 1 cm³?

Saturday, 23 July 2011                              50
     What is the mass of 1cm3 ?
     • Can you work out what the mass would be if
       every block was 1 cm³?

      Material           Mass (g)   Volume   Density
                                    (cm3)    (g/cm3)
      iron

      brass

      aluminium

      lead


Saturday, 23 July 2011                                 51
     What should your results be?
     Material            Density (grams per cm3)

     iron                7.87

     brass               ?

     aluminium           2.7

     lead                11.36

Saturday, 23 July 2011                             52
     So…
     Now you know which material
      was the most dense.



                         Check learning

Saturday, 23 July 2011                53
     Plenary: Any ideas?
     Material            Density (grams per cm3)

     iron                7.87
     brass               ?
     aluminium           2.7
     lead                11.36
     water?
     Copper?
     Wood?
     Cheese?


Saturday, 23 July 2011                             54
Finishing up

•   Save any computer work.
•   Equipment away please.
•   Give in your books.
•   Clear your table.
•   WASH YOUR HANDS!
     Forces: Lesson 6

                Are objects lighter under water?




Saturday, 23 July 2011                             56
     Equipment
     • Objects to weigh underwater
     • Forcemeters




Saturday, 23 July 2011               57
    OBJECTIVES
    & what I am looking for
     • To learn the idea of a     • You can draw a basic force
       force called upthrust.       diagram in 2D.
                                  • You are able to measure
     • To learn how to make         force accurately using a
       accurate measurements        force meter.
       of forces.                 • You can use the computer to
     • To develop your ability      produce a useful graph that
       to explain why things        shows your results clearly.
       happen.                    • You can explain why forces
                                    cause things to be lighter in
     • To correctly mark forces     water.
       on diagrams.               • You can evaluate your test.


Saturday, 23 July 2011                                         58
     What forces?
                                  upthrust




        thrust
                                             drag




                         weight




Saturday, 23 July 2011                              59
 The proper way…
                         upthrust




thrust                              drag




                         gravity
Saturday, 23 July 2011                     60
     Instructions
     • Use the study guide. Write the title & date.
     • Write: What is the force that pulls down on
       the stone? [The force that… ]
     • Draw the diagram in 2 dimensions showing
       the forces correctly.
     • Use the equipment to find out if objects are
       lighter under the water. Repeat each test to
       get accurate results.
     • Record your results in a table.

Saturday, 23 July 2011                                61
     Results
              Object     weight in air   weight under    Difference
                         (NEWTONS)          water       (NEWTONS)
                                         (NEWTONS)




Saturday, 23 July 2011                                                62
     Produce a spreadsheet using a computer. Use
     a formula to calculate the difference column.
            Object       weight in air   weight under    Difference
                         (NEWTONS)          water       (NEWTONS)
                                         (NEWTONS)


             stone            3              2          =B2-C2
         iron block           5             3½




Saturday, 23 July 2011                                            63
     Conclusion & evaluation
     • Explain why the objects were lighter
       under water. Make sure you show your
       knowledge of forces.
     • Evaluate your test.




Saturday, 23 July 2011                        64
     Forces: Lesson 7

             Why are some toy cars faster than
                        others?



Saturday, 23 July 2011                           65
     Equipment
     •   Toy cars
     •   Wooden ramps
     •   Clinometers
     •   Stop watches




Saturday, 23 July 2011   66
     OBJECTIVES
     • To learn why it is        • To do a fair test.
       important to make lots    • To learn why it is
       of measurements.            important to make lots
     • To learn how to explain     of measurements.
       why things happen.        • To explain why a force
     • To learn about friction     called friction affects the
       and drag.                   speed of a car.
                                 • To explain what
                                   happens to the energy.
                                 • To calculate speed.
Saturday, 23 July 2011                                      67
     By the end of the lesson…
     • Be able to peruse, choose and use the
       right equipment.
     • Be able to list the variables.
     • Be able to write an explanation.
     • Be able to measure and calculate
       speed.*


Saturday, 23 July 2011                         68
     Force diagram
                         road
                         holds
                         kart up




                                   friction
                                   and
                                   drag
 thrust



                          weight



Saturday, 23 July 2011                        69
     Forces: Lesson 8

                    Do things float better in salty
                               water?



Saturday, 23 July 2011                                70
     Equipment
     •   Hydrometers
     •   Salty water
     •   Very salty water
     •   Tap water
     •   A ball
     •   Transparent fish tank

Saturday, 23 July 2011           71
     OBJECTIVES / OUTCOMES
     • To learn about           • You can peruse,
       forces that act in         choose and use the
                                  right equipment.
       different directions.
                                • You can measure
     • To develop your            accurately.
       ability to explain why   • You can explain why
       things happen.             forces make this
                                  happen.
                                • You can evaluate your
                                  test.

Saturday, 23 July 2011                                    72
     Starter
     Pushing a ball onto a bucket of water.

     Key questions…
     • As I push the ball down, what happens
        to the water?
     • Does the water have mass? Am I
        lifting it?
Saturday, 23 July 2011                        73
As the ball is pulled
down by gravity, the
water is lifted.




                   The ball will go down until it balances
                   the mass of the water it is pushing out
                   of the way.


Saturday, 23 July 2011                                       74
                         What if the ball was
                         lighter?


                           What if the water was
                           heavier?


                               How could you
                               make the water
                               heavier?
Saturday, 23 July 2011                          75
     Input
     • BBC DVD: Class Clips 1 / Materials &
       their properties / Compounds &
       mixtures / 5 Mixtures




Saturday, 23 July 2011                        76
   VERY
  SALTY
  WATER      SALTY        TAP
             WATER       WATER
                                              diagram          •Use the same
                                                               hydrometer every
                                                               time.
                                              Wooden
                                              dowel
                                                               •Measure how high
                                                               the hydrometer floats
                                              blob of          (in mm from the
                                              plasticine       surface of the water
                                                               to the top of the
                                            water              dowel).

                                         Water type            Height of     Density of water
                                                           hydrometer (mm)

                                 Very salty

                                 Salty

                                 Tap water (no salt)
Saturday, 23 July 2011                                                                 77
     Finishing up
     • Why does the
       hydrometer float
       better in very salty
       water? Write to
       explain why in terms
       of forces.
     • Evaluate your test.

Saturday, 23 July 2011        78
     Forces Lesson 9

                    Is friction sometimes useful?




Saturday, 23 July 2011                              79
     OBJECTIVES / OUTCOMES
     • To learn how friction   • Your two diagrams
       is sometimes a            show that you know
       useful force.             where high friction is
                                 important.
     • To learn where
                               • Your two diagrams
       friction forces           show that you know
       happen.                   where low friction is
     • To learn how to add       important.
       labels and captions.    • You can write useful
                                 captions.
Saturday, 23 July 2011                               80
     Equipment
     • Video: Cycling crazy




Saturday, 23 July 2011        81
     Activities
     • Video: Cycling crazy
     • High friction and low friction (use study
       guide)




Saturday, 23 July 2011                             82
Saturday, 23 July 2011   83
     Rounding up
     • Your two diagrams show
       that you know where high
       friction is important.
     • Your two diagrams show
       that you know where low
       friction is important.
     • You can write useful
       captions.

Saturday, 23 July 2011            84
     Forces Lesson 10

                     Do pulleys help with lifting?




Saturday, 23 July 2011                               85
     Equipment
     •   Pulley sets
     •   Hang on masses
     •   Forcemeters
     •   1kg masses
     •   String



Saturday, 23 July 2011    86
     OBJECTIVES/ OUTCOMES
     • To learn that pulleys      • You can work as a team
       are helpful for lifting.     to set up the test.
                                  • You can use a
                                    forcemeter to measure
                                    the pulling forces.
                                  • You can record your
                                    results in a table.
                                  • You can write to
                                    describe what you
                                    noticed.

Saturday, 23 July 2011                                  87

								
To top