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Force & Motion

Force & 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

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  1. Force & Motion Unit Review

  2. 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

  3. 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)

  4. 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

  5. 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)

  6. 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

  7. 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

  8. 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)

  9. 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

  10. 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)

  11. 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.

  12. 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)

  13. 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

  14. 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

  15. 14. How will an object’s mass affect its possible acceleration? given the same force… • More mass = less acceleration; • less mass = more acceleration

  16. 15. What force most resists motion? • friction

  17. 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

  18. 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

  19. 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.

  20. The test • 20 multiple guess questions • 6 short answer • 1 essay-ish (math related) • ONLY 1class period to complete answer document

  21. Any Questions

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