The Man’s Jeopardy. Learning Objectives. Describe what a force is. Describe how balanced and unbalanced forces are related to an object’s motion. Describe friction and identify the factors that determine the frictional force between 2 objects.
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Forces & Friction
Newton’s Laws 1&2
Newton’s 3rd Law & Momentum
Which of the following is NOT an example of exerting a force on an object: pushing a button, punching a mascot, running to school? What effect do unbalanced forces have on an object’s motion?
Running to School (not exerting a force)
Unbalanced forces change an object’s motion.
An object is falling toward the Earth at 9.3 m/s/s. Why is the object not falling at 9.8 m/s/s? In general, what type of force resists any object’s motion in the opposite direction?
What force typically causes momentum to seem like it was NOT conserved? Example- the collision of two hockey players.
Give an example of how decreasing friction is helpful.
Oiling a machine or bike, waxing a snowboard, using a cart with wheels to move an object
Using the diagram below, what direction is the net force on the object? What is the net force? How could you balance the forces on the object?
Down, 50 N, Increase the upward force by 50 N
The force that acts on all objects on Earth and is the only force acting on an object in free-fall is ___________.
How can the gravitational attraction between 2 objects be decreased?
Lower the mass and spread the objects further apart.
Suppose a planet with a mass of 100.5 x 1024 kg was discovered. Based upon the data above, what is a possible value for the gravitational pull of this new planet?
Any value from 1.1 to 2.3 would be correct. The best values would be between 1.1 and 1.5.
Bob and Joe believe that heavier objects fall faster. They design an experiment to test out their prediction. What is their hypothesis? How should they design the experiment? What is ONE variable that Bob and Joe should try to keep constant? Give answer verbally.
Hypothesis- Heavier objects fall faster.
Design- Drop objects of different masses and determine their acceleration (or the time it takes for them to hit the ground).
Constants- Height of the drop, air/wind resistance (if possible), same timer or timekeeper, etc.
Three satellites are orbiting the Earth. The distance from Earth is 6,000 km for Satellite A; 10,000 km for Satellite B; and 35,800 km for Satellite C. Which one would Earth have the greatest attraction for? Explain why.
Satellite A because it’s the closest.
The ability of an object to resist a change in motion is called ___________.
What types of objects have the greatest inertia? What do objects in motion tend to do? What do objects at rest tend to do?
Objects in motion tend to stay in motion
Objects at rest tend to stay at rest
An object accelerates at 4 meters per second2 for a force of 20 N. How much force is needed for an acceleration of 40 m/s/s for the same object? If the amount of force on a heavy object is the same as the amount of force on a lighter object, then which object will have the lower acceleration?
10x the acceleration for a constant mass = 10x the force, so 200 N
The heavier object will have the lower acceleration.
A 100 kg person is skydiving. What is the force of gravity (or weight) acting on the skydiver?
F = m x a
F = 100 kg x 9.8 m/s/s
F = 980 N
Give two real world examples of Newton’s 1st Law (you may do this verbally instead of writing it down).
A car stops and your body moves forward, a car takes off and your body moves backward, etc.
According to Newton’s 3rd Law, for every action there is an _________ and ________ reaction.
For every action there is anequalandopposite reaction.
What are the action-reaction forces when a carpenter hammers a nail?
Action = hammer striking the nail
Reaction = nail pushes back on the hammer
How is momentum calculated? True or False. Change the underlined word to make it true. The momentum of an object is in the OPPOSITE direction of that object’s velocity.
Momentum = mass x velocity
False, momentum is in the SAME direction as the object’s velocity.
If the total momentum after a collision is 10 kg x m/s, then what was the total momentum before the collision? Explain how you know.
10 kg x m/s because momentum is conserved(remains the same and is not lost, only transferred)
How can an object’s momentum increase? Provide 2 ways.
Moving faster or higher velocity
Greater the mass, the higher the momentum
Draw a force diagram for a person pushing a large oven up a ramp toward the left. Correctly label all of the forces acting on the “box” using arrows of the correct length.