TAKS Objective 5.2 Write down your answers for the next 4 questions. Use the formula chart. Use a calculator. Don’t guess! 1. The diagram represents the total travel of a teacher on a Saturday. Which part of the trip is made at the greatest average speed? AQ BR CS D T 2. 3. How much force is needed to accelerate a 1,300 kg car at a rate of 1.5 m/s2? A 867 N B 1,950 N C 8,493 N D 16,562 N 4. A ball moving at 30 m/s has a momentum of 15 kg·m/s. The mass of the ball is — A 45 kg B 15 kg C 2.0 kg D 0.5 kg Check your answers, if they are all correct, try the quiz at the end . . . 1. C 2. A 3. B 4. D Law of Conservation of Energy Energy can change forms, but is never created nor destroyed Loss in one form = gain in an another form A falling object speeds up as it falls to the ground; PE decreases as KE increases. The KE it has at impact = the PE it had before it fell. Forces and Motion Forces can create changes in motion (acceleration) Deceleration is negative acceleration Force = Mass x Acceleration Units of force are Newtons (N) Motion can be described simply Motion is a change in an object’s position Average velocity (speed) is a change of the position of an object over time Velocity Graphs V = distance time Velocity(v) is Velocity the slope (rise over run) of a 60 Distance (m) position (d) 40 Series1 vs. time (t) 20 Series2 graph 0 1 3 5 7 9 11 13 15 Time (sec) The diagram represents the total travel of a teacher on a Saturday. Which part of the trip is made at the greatest average speed? How do we work this one? Calculate v = d/t for each segment. Acceleration is a change in an objects velocity (speed or direction) When an object’s speed changes over time it is accelerating (or decelerating) A = vfinal – vinitial time Units for acceleration m/s/s or m/s2 Acceleration Graphs Acceleration (a) Acceleration is the slope of a Velocity ((m/s)(m) velocity (v) vs. 60 time (t) graph 40 Plotted on a 20 distance vs. time 0 graph, 1 3 5 7 9 11 13 15 acceleration is Time (sec) an exponential curve Definition of a Force A Force is a push or a pull Balanced Force A force that produces no change in an object’s motion because it is balanced by an equal, opposite force. Unbalanced Forces Are forces that results in an object’s motion being + changed. Friction A force that acts in a direction opposite to the motion of two surfaces in contact with each other. Friction Friction causes an object to slow down and stop. Since the amount of energy stays constant, the energy becomes heat. Newton’s 1st Law of Motion Object in motion stays in motion Newton’s 1st Law of Motion And Objects at rest stay at rest Newton’s 1st Law of Motion they are acted upon by Until unbalanced forces. Law of Inertia is another name for Newton’s 1st Law Tendency for an object to stay at rest or moving in a straight line at a constant speed. The mass (m measured in kg) of an object determines its inertia Unit of Force – Use the chart Unit of mass is kg Unit of Acceleration is m/s/s 1 kg x 1 m/s/s = 1 kg x m/s/s = 1 Newton (N) Resulting in Force unit called a Newton (N) Newton’s 2nd Law or the Law of Acceleration Force = Mass X Acceleration F=ma Weight (pull of gravity) is a commonly measured force, calculated by F=mg, g is the acceleration due to gravity 9.8 m/s2 Same floor = same friction Same room = same air Same car = same mass Newton’s 2nd Law of Motion The greater the mass of an object, the greater the force required to change its motion. Newton’s 2nd Law of Motion Thegreater the acceleration of an object, the greater the force required to change its motion. Your Turn! How much force is needed to accelerate a 1,300 kg car at a rate of 1.5 m/s2? To solve this: F=ma or = 1300Kg x 1.5m/s2 F = 1950 N Newton’s 3rd Law of Motion Forevery action force there is an equal and opposite reaction force. Newton’s 3rd Law of Motion All forces come in action- reaction pairs Ex: feet push backward on floor, the floor pushes forward on feet Newton’s 3rd Law of Motion Rocket and Jets- walls of the fuel compartment push backward on igniting gases, gases push forward on the fuel compartment (and the rocket) so it rises. Newton’s 3rd Law of Motion Rowing a boat Name the Action Reaction pair of forces? Action: Oar pushes water back. Reaction: water pushes boat forward. Machines do Work Work: the product of force times distance W=Fxd The work done by forces on an object = changes in energy for that object. work and energy are measured in Joules 1 Joule=1 Newton • meter Machines make work easier The ideal mechanical advantage of a machine (IMA) is the number of times the output force is larger than the input force IMA=Fout/Fin A machine can only make this happen by moving the input force a farther distance than the output force Fin • din=Fout • dout Real Machines use Energy No real machine is 100 % efficient. i.e. none put out more work than is put in Efficiency of a machine is work output/work input X 100 % Eff = Wout X 100% W in Machines use power Power: the rate at which energy is used (work is done) P=Work/time Power is measured in H.P. or watts 1 watt = 1 Joule 1 sec 6 Types of simple machines Some Simple Machines: Inclined planes Screws Pulleys Wheel and axle Levers Wedge Universal Law of Gravitation All objects in the universe attract each other by the force of gravity Universal Law of Gravitation 1) the mass of the object doing the pulling, and Gravity varies depending on two factors: 2) the distance from the center of that object On Earth gravity = 9.8 m/s/s Forevery second that an object falls its speed increases by 9.8 m/s Weight= Mass (m) X acceleration due to gravity (g) Weight Unit of mass = kg Unit of acceleration = m/s/s Unit of weight = Newton 1 Newton= about ¼ pound_ Last quiz! For the next 7 slides, write the answers on your own paper. Label this one Obj. 5.2 If you have time, check out TAKS Dr. Try to answer each question, and then see the answer and why it is correct. This is the practice test you took in September. GOOD LUCK! 1. The frog leaps from its resting position at the lake’s bank onto a lily pad. If the frog has a mass of 0.5 kg and the acceleration of the leap is 3 m/s2, what is the force the frog exerts on the lake’s bank when leaping? A 0.2 N B 0.8 N C 1.5 N D 6.0 N 2. If a force of 100 newtons was exerted on an object and no work was done, the object must have — A accelerated rapidly B remained motionless C decreased its velocity D gained momentum 3. How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N? A 300 J B 750 J C 1,000 J D 15,000 J 4. 5. 6. Which lever arrangement requires the least effort force to raise a 500 N resistance? A. C. B. D. 7. The illustration below shows a student standing on a skateboard about to throw a ball. Which picture correctly shows the movement of the skateboard after the release of the ball? The End…Check your answers . . . 1. C 2. B 3. A 4. C 5. A 6. A 7. D Turn in your answers with your name and your teacher’s name on it. Now its your turn. Work through problems in the workbooks, ask for help if you need to from any science teacher, and attend the tutorials for objectives on which you did not score 100%.