Chapter 4 Review Questions Key Terms Page 56 #1-20

Chapter 4 Key Terms pp.56 Equilibrium: in general, a state of balance. The state of a body which no net force acts. When an object is at rest, with the net force being zero. Force: any push or pull, SI unit is the Newton, force is what causes a mass of 1 kilogram to accelerate at a rate of 1 meter per second squared

Chapter 4 Key Terms Friction: the force that acts between materials that touch as they move past each other. A force that acts to resist the motion of objects in contact with one another. Inertia: the reluctance of any object to resist its change in motion. Mass is a measure of inertia Kilogram: a unit of measurement of mass.

Chapter 4 Key Terms Law of inertia: Newton’s first law of motion. Every object continues in a state of rest, or of uniform motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it. Mass: a measure of inertia, the amount of matter in an object. Net Force: the combination of all forces acting on an object.

Chapter 4 Key Terms Newton: the SI unit of force, symbolized by a capital N. Newton’s First Law: also called the law of inertia, a restatement of Galileo’s ideas Normal force: for an object resting on a horizontal surface, the upward force that balances the weight of the object, also called the support force.

Chapter 4 Key Terms Support Force: also called the normal force, the force which acts at right angles to the surface, the force which balances out another force causing a net force of zero. Weight: the force of gravity on an object, mass and weight are proportional to each other in a given place, but not equal to each other, how strongly matter is attracted by gravity.

1. What distinction did Aristotle make between natural motion and violent motion? (4.1) Natural motion is straight up or straight down, circular for planets and stars. Objects seek their natural resting place. The Earth’s natural motion was thought to be at rest. Violent motion is imposed, a result of forces that pushed or pulled.

2. Why was Copernicus reluctant to publish his ideas? (4.2) Copernicus feared persecution. He formulated the theory of the “moving Earth”. The Heliocentric Theory: the sun was the center of our solar system. With his friends encouragement, Copernicus did publish his ideas before he died.

3. What is the effect of friction on a moving object? (4.3) Friction slows motion. Remember Galileo and Newton who proposed the idea that an object only requires a force to overcome friction and to initially set an object in motion.

4. The speed of a ball increases as it rolls down an incline and decreases as it rolls up an incline. What happens to its speed on a smooth, horizontal surface? (4.3) Neglecting drag and friction, the speed of a ball on a smooth, horizontal surface does not change.

5. Galileo found that a ball rolling down one incline will pick up enough speed to roll up another. How high will it roll compared with its initial height? (4.3) If there is no friction, the ball will roll to the same height as its initial height.

6. Does the law of inertia pertain to moving objects, objects at rest, or both? Support your answer with examples. (4.4) Both. Newton’s first law of motion states that every object continues in a state of rest, or its uniform motion in a straight line, unless it is compelled to change that state by forces exerted upon it. Examples?

You have to keep pedaling to overcome friction. 7. The law of inertia states that no force is required to maintain motion. Why, then, do you have to keep pedaling your bicycle to maintain motion? (4.4) You have to keep pedaling to overcome friction.

8. If you were a spaceship and launched a cannonball into frictionless space, how much force would have to be exerted on the ball to keep it going? (4.4) None. There is no friction or air resistance in outer space to hinder the motion of the cannonball. Therefore, once an object is set in motion it continues in that state of motion unless acted on by other forces.

Mass, inertia, and weight are all directly proportional to each other. 9. Does a 2-kilogram rock have twice the mass of a 1-kilogram rock? Twice the inertia? Twice the weight (when weighed at the same location)? (4.5) Yes Mass, inertia, and weight are all directly proportional to each other.

Volume is how much space an object or substance occupies. 10. Does a liter of molten lead have the same volume as a liter of apple juice? Does it have the same mass? (4.5) Yes, a liter of a substance has the same volume as a liter of another substance. Volume is how much space an object or substance occupies. No, they do not have the same mass. Lead has a different atomic structure than apple juice and therefore does not have equal mass.

11. Why do physicists say that mass is more fundamental than weight? (4.5) Mass is more fundamental because it is independent of location, while weight is dependent on the location’s gravitational force.

12. An elephant and a mouse would both have zero weight in gravity-free space. If they were moving toward you with the same speed, would they bump into you with the same effect? Explain (4.5) No, they would not. There masses are not zero and are very different. Since the elephant has more mass it also has more inertia and would be more difficult to stop.

13. What is the weight of 2 kilograms of yogurt? (4.5) Here on Earth the weight of 2 kilograms of anything is equal to 19.6 N. W = m x g W= 2 kg x 9.8 m/s2 W = 19.6 N

If the object is in equilibrium the resultant force is zero. 14. What is the net force or, equivalently, the resultant force acting on an object in equilibrium? (4.6) If the object is in equilibrium the resultant force is zero.

15. Forces of 10 N and 15 N in the same direction act on an object 15. Forces of 10 N and 15 N in the same direction act on an object. What is the net force on the object? (4.6) The net force is 10 N + 15 N = 25 N

15. Forces of 10 N and 15 N act in opposite directions on an object 15. Forces of 10 N and 15 N act in opposite directions on an object. What is the net force on the object? (4.6) 15 N – 10 N = 5 N

The tension is double when hanging with one arm. 17. How does the tension in your arms compare when you let yourself dangle motionless by both arms and by one arm? (4.7) The tension is double when hanging with one arm.

18. A clothesline is under tension when you hang from it 18. A clothesline is under tension when you hang from it. Why is the tension greater when the clothesline is strung horizontally than when it hangs vertically? (4.8) The vertical components of the tension vector must add up to the weight, so the vectors along the rope will be very large.

19. If you hold a coin above your head while in a bus that is not moving, the coin will land at your feet when you drop it. Where will it land if the bus is moving in a straight line at constant speed? Explain. (4.9) The coin will land at your feet because there is no horizontal acceleration.

20. In the cabin of a jetliner that cruises at 600 km/h, a pillow drops from an overhead rack into your lab below. Since the jetliner is moving so fast, why doesn’t the pillow slam into the rear of the compartment when it drops? What is the horizontal speed of the pillow relative to the ground? Relative to you inside the jetliner? (4.9) The pillow does not slam into the rear of the plane because it is moving at the same horizontal speed of the plane 600 km/h. The horizontal speed of the pillow relative to the ground is the same as the plane 600 km/h. Since you are moving at the same horizontal speed as the plane and the pillow, the pillow moves at a horizontal speed of 0 km/h relative to you as it drops into your lap.