Unit Review

FORCE & MOTION

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?

• 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

Time (s)

Distance (m)

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

Time (min)

Distance (m)

1 2

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

15. WHAT FORCE MOST RESISTS MOTION?

• friction

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 1 class period to complete answer document

ANY QUESTIONS