Friction and Air Resistance

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

• opposite to the direction of sliding

• in the same direction as the forces that produces sliding

• usually at right angles to the force that produces sliding

• non-directional

A crate sits at rest on a factory floor. Friction between the crate and floor occurs

• only if the crate is sliding

• only if the crate is pushed vertically as well as horizontally

• when the crate is pushed horizontally, whether sliding or not

• even when no pushing occurs

Tags

NGSS.MS-PS2-2

When you push horizontally on a crate that doesn't slide on a level floor, how great is the force of friction on the crate?

• The friction force is equal to and in the same direction as your push

• The friction force is equal and opposite to your push

• The friction force is equal to the mass of the create times its acceleration

• The friction force is zero

Tags

NGSS.HS-PS2-1

As you increase your push on a stationary crate, will friction on the crate increase also?

• The friction force remains zero

• The friction force decreases and is in the opposite direction as your push

• The friction force increases and in the same direction as your push

• The friction force increases and is opposite in direction to your push

Once the crate is sliding, how hard do you push to keep it moving at constant velocity?

• You push with a force slightly greater than the static friction force

• You push with a force equal to and opposite the dynamic friction force

• You no longer need to push once the crate is sliding

• You push with a force slightly greater than the dynamic friction force

Tags

NGSS.HS-PS2-1

Which is normally greater: static friction or sliding friction on the same object?

• Static friction is normally greater than dynamic friction

• On the same object, static friction and dynamic friction are equal

• Dynamic friction is normally greater than static friction

• Static friction and dynamic friction are both zero

Which is the condition for an object experiencing free fall?

• When there are no horizontal forces on an object it is in free fall

• When the net force on an object is equal and opposite to the gravity force, the object is in free fall

• When gravity is the only force acting on an object, it is in free fall

• When the net force on an object is zero, it is in free fall

Why doesn't a heavy object accelerate more than a light object when both are freely falling?

• The inertia of the heavy object is just enough smaller than the inertia of the lighter object to counteract the larger gravity force

• The ratio of the weight to mass is the same for all object in the same locality

• The inertia of the heavy object equals the inertia of the lighter object, so their accelerations are the same

• The larger air resistance force on the larger object makes it fall with the same acceleration

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4

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

• They both free fall equally

• The force of gravity is in the same on each

• The ratio of weight to mass is the same for each

• Air resistance has no effect

Tags

NGSS.HS-PS2-4

As a skydiver gains speed in falling through the air, air resistance...

• Increases

• Decreases

• Becomes negligible when terminal speed is reached

• Cancels weight

Tags

NGSS.HS-PS2-4