Physics- Newton's 2nd and 3rd Laws

Which of the following depends on gravity?

Weight

Newton's second law of motion.

The acceleration of an object is directly proportional to the net force acting on an object, is in the same direction as the net force, and is inversely proportional to the mass of an object.

If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?

Acceleration depends on the mass, so the smaller the mass, the greater the acceleration and vice versa.

Is acceleration directly proportional to mass, or is it inversely proportional to mass? Give an example.

Acceleration is inversely proportional to mass. For example, if the mass of an object were to increase, then acceleration decreases. If mass was doubled, then the acceleration is cut in half.

Is acceleration proportional to net force, or does acceleration equal net force?

Acceleration is proportional to net force. If you double the net force of an object, the acceleration doubles, so acceleration depends on the net force.

How many forces are required for an interaction?

An interaction is forces between one thing and another. They require a pair of forces acting on two different objects.

A block of mass 2kg is acted upon by two forces: 3N (directed to the left) and 4N (directed to the right). What can you say about the block's motion?

It could be moving to the left, moving to the right, or be instantaneously at rest.

What relationship does mass have with weight?

Mass and weight are directly proportional to each other. For example, if the mass was tripled, then the weight would be tripled and so on. Mass and weight are often interchanged because of their similarities.

Clearly distinguish among mass, weight, and volume.

Mass is how much matter an object has. Weight is the force on an object due to gravity. Volume is the size of the object.

Which is more fundamental, mass or weight? Which varies with location?

Mass is more fundamental. Weight varies with location because, for example, you would have a different weight on the moon than on Earth because the acceleration of gravity would be different on the moon. Weight depends on gravity.

Slide a block on its widest surface, then tip the block so it slides on its narrowest surface. In which case is friction greater?

Neither, the friction will remain the same no matter what side you slide the block on.

Which of the three laws deals with interactions?

Newton's third law of motion

What relationship does mass have with inertia?

The greater the mass, the greater the inertia. An object with a lot of mass will have a lot of inertia.

A Volkswagen bug and a Volvo truck have a head-on collision. Which statement is true?

The magnitudes of both forces are the same

If a block is moving to the left at a constant velocity, what can one conclude? Hints

The net force applied to the block is zero

What is the net force that acts on a 10-N freely falling object?

The net force is 10 N.

Consider hitting a baseball with a bat. If we call the force on the bat by the ball the action force, identify the reaction force.

The reaction force would be the force of the ball on the bat.

When you push against a wall, what pushes back?

The wall

Consider the apple and the orange (in the following figure). If the system is considered to be only the orange, is there a net force on the system when the apple pulls?

There is no net force because the apple is outside of the system. The force may affect the apple, but will not affect the orange.

When you push against a wall with your fingers, they bend because they experience a force. Identify this force.

When you push against a wall with your fingers, the wall is pushing back on you. That is why your fingers bend.

Newton's third law of motion.

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

As you read this, how fast are you moving relative to the chair you are sitting on? Relative to the Sun?

You are not moving relative to the chair, but you are moving 107,000 km/h relative to the sun.

Two forces, of magnitude 4N and 10N, are applied to an object. The relative direction of the forces is unknown. The net force acting on the object __________.

cannot have a magnitude equal to 5N

Fill in the blanks: Newton's first law is often called the law of__________; Newton's second law is the law of__________; and Newton's third law is the law of __________ and __________.

inertia, energy, action and reaction

In considering proportions, acceleration is _______.

inversely proportional to mass

A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________.

moving with a constant nonzero acceleration

The direction of the force of friction on a sliding crate is _______.

opposite to the direction of sliding

When hitting a tennis ball with your racquet, the force on the ball has the same magnitude as the force on the _______.

racquet

The unit of mass is the kilogram, and the unit of weight is _______.

the newton

A 1-kg stone and a 10-kg stone have the same acceleration in free fall because _______.

the ratio of weight to mass is the same for each

Whenever a net force acts on an object, there is a change in the object's _______.

velocity