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Force &amp; Motion

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# Force &amp; Motion - PowerPoint PPT Presentation

Force &amp; Motion. Unit Review. 1. Explain how a parachute slows the rate of a skydivers fall. The use of friction of air being caught by the chute…called air resistance. 2. If a bowling ball and a marble are pushed with the same force, which one will move faster? Why ?.

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### Force & Motion

Unit Review

• The use of friction of air being caught by the chute…called air resistance
2. If a bowling ball and a marble are pushed with the same force, which one will move faster? Why?
• The marble will move faster due to less mass (a = F/m: Bowling ball has more mass and therefore will accelerate slower)
3. Describe balanced and unbalanced forces.
• Balanced forces are equal causing no acceleration; happens when objects are at rest or when moving objects are at constant velocity
• Unbalanced force are unequal an cause acceleration in the direction of the larger force
4. Define acceleration.
• Measure of the change in motion of an object (change in speed and/or direction: positive acceleration = speed up; negative acceleration = slow down; turn = change directions)
5. Can an object be in motion and not be accelerating? Explain your answer.
• YES! An object such as a car moving at a constant velocity (same speed, same direction) has balanced forces acting on it
6. What is the mass of an object that is accelerated at a rate of 10 m/s2 with a force of 30N?
• m = F/a
• m = 30 N / 10 m/s2
• m = 30 kg-m/s2 / 10 m/s2
• m = 3 kg
7. Draw a distance/time graph that shows an object traveling at a constant speed. How would you know if the object changed speeds?
• [graph should have a straight line from lower left to upper right]
• change in speed would be represented by a change in the slope of the line

Distance (m)

Time (s)

8. Define velocity. How is velocity different than speed?
• Velocity is how fast something is going and in what direction; i.e., it IS speed with a directional component
9. Define and explain each of Newton’s 3 laws.
• 1st – Law of Inertia: objects at rest stay at rest & objects in motion stay in motion at constant velocity unless acted on by another force; balanced forces cause resting objects to stay resting and moving objects to keep moving at constant velocity; unbalanced forces cause resting objects to move and moving objects to accelerate (change speed and/or direction)
• 2nd – Law of Acceleration: the acceleration on an object is related to the force applied to it divided by the objects mass (a = F/m); the more mass an object has, the more Force required to cause its acceleration
• 3rd – Law of Action/Reaction: for every action force, there is a reaction force = in strength and opposite in direction; forces always exist in pairs (like muscles)
10. Describe 3 action-reaction pairs that demonstrate Newton’s 3rd law.
• Any 3 examples that show a force pair pushing on each other: i.e., rocket launch, push on wall & it pushing back; you push on ground, ground pushes you so skateboard goes forward, etc.
11. Draw a distance-time graph showing an object traveling at a constant speed and then stopping after 2 min.
• [graph shows a straight, diagonal line going from lower left to upper right and the flat (parallel to x-axis) at the 2 min mark

Distance (m)

1 2

Time (min)

12. Suppose you are riding on your bike at 10 km/hr when you hit a wall. Describe your motion at the moment of impact using Newton’s laws.

• 3rd: bike pushes wall, wall pushes bike;
• 1st: person keeps moving forward though bike is stopped;
• 2nd: the Force applied to the wall = mass of the bike and person divided by the acceleration of them
13. What is the relationship between mass, force and acceleration?
• Several possibilities, but most important: for the same force, as mass increases, acceleration decrease; for acceleration to increase, mass would have to decrease (inversely proportional); given same mass, more force = more acceleration; given same acceleration, more mass would require more force
14. How will an object’s mass affect its possible acceleration?

given the same force…

• More mass = less acceleration;
• less mass = more acceleration
16. What is the force that a 10 kg book exerts on your desk? [Note: Acceleration due to gravity = 9.8 m/s2]
• F = ma
• F = 10 kg x 9.8 m/s2
• F = 98 kg-m/s2
• F = 98 N

17. You are driving north on I35E to Oklahoma City at a speed of 80 km/hr. It takes you 4 hours to get there. How far is it from here to Oklahoma City?

• d = st (from s = d/t)
• d = 80 km/h x 4 hr
• d = 320 km
NOTES:
• Know the differences between speed, velocity, distance and displacement.
• Be able to interpret a displacement-time graph (like your quiz).
• Be able to calculate speed, velocity and acceleration.
• Know Newton’s 3 laws and how they apply to everyday situations.
The test
• 20 multiple guess questions
• 6 short answer
• 1 essay-ish (math related)
• ONLY 1class period to complete answer document