Newton's Second Law of Motion

Flashcards reviewing Newton's Second Law of Motion, covering force, acceleration, mass, friction, pressure, free fall, and air resistance.

What causes acceleration?

The cause of acceleration is force.

What causes an object to accelerate?

Unbalanced forces acting on an object.

How do you increase the acceleration of an object?

Increase the net force acting on it.

What is the relationship between acceleration and net force?

An object's acceleration is directly proportional to the net force acting on it.

What does an increase in mass result in for a constant force?

A decrease in acceleration.

What is the relationship between acceleration and mass?

The acceleration is inversely proportional to the mass.

What is Newton's Second Law?

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

What is the formula for Newton's Second Law?

Acceleration = Net Force / Mass

If a car can accelerate at 2 m/s^2, what acceleration can it attain if it is towing another car of equal mass?

1 m/s^2

A car has a mass of 1000 kg. What is the acceleration produced by a force of 2000 N?

2 m/s^2

If the force is 4000 N, what is the acceleration, given the car's mass is 1000 kg?

4 m/s^2

How much force must a 30,000-kg jet plane develop to achieve an acceleration of 1.5 m/s^2?

45,000 N

What does the force of friction between surfaces depend on?

The kinds of material in contact and how much the surfaces are pressed together.

How does friction act on materials that are in contact with each other?

It always acts in a direction to oppose relative motion.

What is a free-body diagram?

A diagram showing all the forces acting on an object.

Two forces act on a book resting on a table: its weight and the support force from the table. Does a force of friction act as well?

No, not unless the book tends to slide or does slide across the table. Friction forces occur only when an object tends to slide or is sliding.

What is pressure?

The amount of force per unit of area.

What is the formula for pressure?

P = F/A (Pressure = Force / Area)

How does the area of contact affect the pressure a force exerts on an object?

The smaller the area supporting a given force, the greater the pressure on that surface.

In attempting to do the bed-of-nails demonstration, would it be wise to begin with a few nails and work upward to more nails?

No, no, no! The resulting greater pressure would cause harm.

Why do all freely falling objects fall with the same acceleration?

The net force on an object is only its weight, and the ratio of weight to mass is the same for all objects.

What does the air resistance force an object experiences depend on?

The object's speed and area.

What is the relationship between air resistance force, speed and frontal area?

Air resistance force is directly proportional to the speed and frontal area of an object.

What is terminal speed?

The speed at which the acceleration of a falling object is zero because friction balances the weight.

Which experiences a greater air resistance force, a falling piece of paper or a falling elephant?

The elephant! It has a greater frontal area and falls faster than a piece of paper.

If a heavy person and a light person open their parachutes together at the same altitude and each wears the same size parachute, who will reach the ground first?

The heavy person will reach the ground first.

When will an object accelerate?

An object will accelerate when it is pushed or pulled with a net force.

When a net force acts on an object, what does its acceleration depend on?

When a net force acts on an object, its acceleration depends on the object's mass.

A cart is pushed and undergoes a certain acceleration. How would the acceleration compare if it were pushed with twice the net force while its mass increased by four?

If a cart is pushed with twice the net force while its mass increased by four, its acceleration would be half.

Where does friction occur?

Friction occurs in solids sliding over one another, fluids, and air.

When you stand on one foot instead of two, what is the pressure you exert on the ground?

When you stand on one foot instead of two, the pressure you exert on the ground is twice.

Why does a 20-kg rock fall no faster than a 10-kg rock in free fall?

The reason a 20-kg rock falls no faster than a 10-kg rock in free fall is that the force/mass ratio is the same.

Kevin and Suzanne go sky diving. Kevin is heavier than Suzanne, but both use the same size parachute. Why does Kevin have a greater terminal speed compared with Suzanne?

Kevin has a greater terminal speed compared with Suzanne because he has to fall faster for air resistance to match his weight.