Physics Ch 4

What is weight? Is it the same as mass? If not, what is the difference?

Weight is net gravitational force. Weight is not the same as mass because is its quantity in inertia while weight is force due to gravity

"Planet earth is pulled upward toward a falling boulder with just as much force as the boulder is pulled downward earth" true or false? why?

True because two forces are equal but opposite in direction.

Is an object's acceleration always in the same direction as its velocity (its direction of motion)? If not, give an example in which it is now. Is an object's acceleration always in the same direction as the net force on the object? If not, give an example in which it is not.

-No! for example, when a car slows down, the change in speed is opposite from motion. -Yes! the object's acceleration is always in the same direction as the net force.

As we know, "weight" is a force, and force is an interaction. In the case of your own weight, name the two objects that are involved in this interaction.

1. You 2. Earth

As you increase the net force on an object, what happens to its acceleration? What if you double the net force? As you increase the mass of an object (for example, by gluing additional matter to it), what happens to its acceleration? what if you double the mass?

Acceleration also increase. If net force is doubled, acceleration also doubles. If mass increases, then acceleration decreases. If mass doubled, then acceleration becomes half.

If you exert a force on an object and then exert three times as strong a force on the same object, what (if anything) can you say about the object's acceleration during the exertion of each force? assume no other force acting on the object.

Acceleration is directly proportional to force. Therefore, acceleration exert 3X.

Since the law of inertia states that no force is needed to keep an object moving in a straight line at an unchanging speed, why is a force needed to keep a car moving?

Because there are some force that appose its motion. In order to cancel these, car need force in order to move in a straight line at an unchanging speed.

Which has the greater mass, a tonne of feathers or a tonne of iron? weight? larger volume?

Both has the same mass and weight., but volume of feather is greater than volume of iron because iron has more density.

A car starts up from rest, moving along straight highway with an acceleration of 1m/s^2. A second car comes racing past at a steady 120km/hr. Which car has the larger net force acting on it?

Car number 2 larger net force because it is going faster.

"Planet earth is pulled toward a falling boulder with just as much acceleration as the boulder is pulled toward earth" true or false? why?

False because acceleration is inversely proportional to mass. boulder has larger acceleration than earth.

When you move an object from Earth to the moon, does its inertia change? weight? mass? amount of matter? Does its acceleration differ while falling freely? Does it respond differently to a net force of 1 N?

Inertia doesn't change bc mass isn't changing. Weight changes bc of gravity. Amount of matter doesn't change. Acceleration while falling freely changes. It responds the same to a net force of 1N on moon.

What do we mean when we say that one object has "more inertia" than another object?

It has more mass.

An astronaut on the moon picks up a large rock. Would it be easier, or harder, or neither for him to pick it up on earth?

It will be harder because gravity on earth is greater on earth.

An astronaut on the moon kicks (horizontally) a large rock. What if she kicked the same rock on earth? Neglecting friction effects, would it hurt her foot more, or less, or just as much?

It will be the same because the astronaut is applying the same force.

Would you rather have a hunk of gold whose weight is 1kg on the moon or one whose weight is 1kg on th earth- or wouldn't it make any difference?

Since the mass doesn't change, it doesn't matter.

A pitcher exerts a force on a baseball while throwing it. Describe the other membrane of the force pair.

The other membrane of the force pair is the force exerted by the baseball on the pitcher.

An object is at rest. Does it then have no force acting on it? Explain. Does it have no net force acting on it?

There are force acting on it because gravitational force acts downward. There's no net force acting on it because object is at rest.

An object moves with unchanging speed in a straight line. Does it then have no force acting on it? Explain. Does it have no net force acting on it?

There are force acting on it. Net force is zero because forward forces are equal to backward forces.

Would you rather have a hunk of gold whose weight is 1N on the moon or one whose weight is 1N on th earth- or wouldn't it make any difference?

Would rather have a hunk of gold in moon. The gravitational pull on earth is greater than moon. Therefore, if both objects have same weight in Newton then gold in moon has larger mass.

A horizontally moving bullet slows down. Is anything exerting a force on it? how do you know? Is it exerting force on anything? how do you know?

Yes because air is the exerting force. Air is exerting in the direction of the bullet's acceleration. Bullet is also exerting force because of the "law of force pairs"

Is any force exerted on you when you speed up along straight line? slow down? how do you know?

Yes, force exerted when you speed up and slow down because there is acceleration.

Is any force exerted on you while you move in a circle at unchanging speed? how do you know?

Yes, force exerted while moving in circle with constant speed because velocity changes. So it's needed to accelerate bc velocity changes.