# Lab by hedongchenchen

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Phys 221              Lab Activity: Experiencing Newton’s Laws
Names: __________________

Experiencing Newton’s Laws
This is a group write up. It must be word-processed. All graphs (which can be neatly
drawn by hand) must be integrated into the text.

Note: if you use this word file as a template, make sure you put all your answers in italic
or boldface such that I can easily distinguish between your work and the template.

The lab report will be due next week Thursday. Drafts are encouraged next week
Monday.
Phys 221              Lab Activity: Experiencing Newton’s Laws
Names: __________________
Part 1: How do you win at Tug O’ War?
“The following two statements are true. In Tug of War:
1. Each team pulls equally hard on the other.
2. The team that wins pushes harder on the ground.”
A. Get together with another group and play a “safe” round of tug of war. Play on two
different surfaces to check out different friction effects. (e.g. socks vs. shoes on the
lab floor or grass vs. cement outside)
B. Consider each team as a unit. Draw a free body diagram of each team.

FBD for team 1                                         FBD for team 2

Surface for team 1: ___________________        Surface for team 2: ___________________

FBD for team 1                                         FBD for team 2

Surface for team 1: ___________________        Surface for team 2: ___________________

C. Refer specifically to the diagrams to write a paragraph discussing how the two
statements above are true.
Phys 221              Lab Activity: Experiencing Newton’s Laws
Names: __________________
Part 2: The Mystery of Salami & Spring Scales

A. Below is a figure showing the three basics salami positions. If the Salami has a mass
of 200 grams predict what the scale reading will be for each situation.

Prediction:
i. Hanging Salami - Scale Reading =          _______
ii. Salami & the Wall - Scale Reading =      _______
iii. Salami vs. Salami - Scale Reading =     _______

Case i

Case ii
200g

200g

Case iii
200g                                   200g

B. Set up the three situations and record the scale reading.

Experimental Result:
i. Hanging Salami - Scale Reading =           _______
ii. Salami & the Wall - Scale Reading =      _______
iii. Salami vs. Salami - Scale Reading =     _______
Phys 221             Lab Activity: Experiencing Newton’s Laws
Names: __________________
C. Draw FBDs for the salami(s) and the scale in each situation. (Ignore the weight of
the scale; the strings were manufactured by our very own massless, frictionless lab
techs )
FBD for salami case i                               FBD for scale case i

FBD for salami case ii                                FBD for scale case ii

FBD for left salami case iii FBD for right salami case iii          FBD for scale case iii

D. Write a paragraph explaining why the scale readings are what they are. Refer to your
force diagrams.
Phys 221             Lab Activity: Experiencing Newton’s Laws
Names: __________________
Part 3: How to get that piece of paper stuck under that book?

A. Place a sheet of paper under your physics text. Observe what happens when you pull
fast on the sheet of paper and when you pull slowly on the sheet paper.

Observations:

B. Draw a free body diagram for the book for each of these situations. You might also
want to draw a FBD for the piece of paper if it helps you visualize the situation.

FBD for book when pulling slowly            FBD for paper when pulling slowly

FBD for book when pulling fast              FBD for paper when pulling fast

C. Write a paragraph explaining the difference between the two situations.
Phys 221              Lab Activity: Experiencing Newton’s Laws
Names: __________________
Part 4: Measuring the G’s in an Elevator

A. Go to the elevator with your group, a spring bathroom scale, and a force plate. One
person in the group will ride the elevator one time on the scale and a second time on
the force plate. During the first ride, the others will read the bathroom scale and write
down the data. During the second ride, they will record the data with the TI
calculator. Before going to the elevator, ask me to show you how to set up the force
plate with Lab Pro and the TI calculator.

B. Take the maximum/minimum scale readings while the elevator is doing the
following:
i. not moving -
ii. starting upwards -
iii. going upwards -
iv. stopping upwards -
v. starting downwards -
vi. going downwards -
vii.    stopping downwards -

C. Record the same complete same ride with the force plate.

D. Back in the lab, view the force plate measurements with LoggerPro. Make a free
body diagram the person riding the scale in each situation.

E. Calculate the magnitude and direction of the net force on the person in each situation.
Use the force plate readings, and check that they match the bathroom scale
measurements.

F. Calculate the person’s mass.

G. Calculate the person’s acceleration (magnitude & direction) in each situation.

H. Calculate the # of “g’s” the person experiences in each situation (=a/g).

I. Write a paragraph which connects the direction of the acceleration you’ve found
        
using dynamics ( Fnet  ma ) to the definitions for acceleration we used in
kinematics (slowing down in the positive direction, etc.
Phys 221             Lab Activity: Experiencing Newton’s Laws
Names: __________________
Part 5: Fun with Balloons (to do outside of the lab hours)

A. Obtain from your local physics department a helium balloon

B. I recommend that you do the experiment on a bus. You can also do it in a car with all
of its windows closed. But if you do it in a car, the driver should not be the person
doing the experiment. You must make sure that the balloon doesn’t interfere with the
driving of the car and that all safety rules are observed (seat belts, etc…). An empty
parking lot would be best to do the experiment in a car.

C. Write down how the balloon reacts to the following situations:
i. Speed up fairly quickly.
ii. Slow down fairly quickly.
iii. Turn to the right in a circle.
iv. Turn to the left in a circle.

D. Write a paragraph which describes the results of your experiment and explains in
terms of Newton’s first, second laws and air pressure differences why the balloon
reacts as it does.

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