U2.FI.MC.FRICTION AND MOTION

Why might adding oil to a machine decrease the friction between its moving parts?

• A. It increases the weight of the machine.

• B. It smooths out rough surfaces and reduces direct contact.

• C. It creates more heat.

Answer explanation

Adding oil smooths out rough surfaces between moving parts, which reduces direct contact and friction. This allows the machine to operate more efficiently and with less wear on its components.

A wooden block slides down a smooth vs. a rough surface. Which statements explain the difference in movement?

• A. The smooth surface creates more friction, slowing the block.

• B. The rough surface creates less friction, speeding the block.

• C. The smooth surface has less friction, allowing faster movement.

Answer explanation

The smooth surface has less friction compared to the rough surface, which allows the wooden block to slide down faster. Less friction means less resistance to movement.

In which situation would increasing friction be beneficial?

• A. Skateboarding on smooth ice.

• B. Riding a bicycle on a gravel path.

• C. Driving on a wet road.

Answer explanation

Increasing friction is beneficial when driving on a wet road, as it helps improve traction and control, reducing the risk of skidding. In contrast, smooth ice and gravel paths require less friction for better movement.

Which factor would increase friction between two surfaces?

• A. Making the surfaces smoother.

• B. Reducing the weight on the surfaces.

• C. Increasing the roughness of the surfaces.

Answer explanation

Increasing the roughness of the surfaces enhances interlocking between them, which raises friction. Smoother surfaces, less weight, and lubricants reduce friction instead.

Why do car tires have tread patterns rather than being completely smooth?

• A. Treads reduce the friction between the tire and the road.

• B. Treads increase friction, helping the car grip the road better.

• C. Treads help make the tires look more attractive.

Answer explanation

Treads increase friction between the tire and the road, which enhances grip and improves vehicle control, especially in wet or slippery conditions. This is crucial for safety and performance.

A sled is moving over three different surfaces: smooth ice, snow, and gravel.

How will the sled move on each surface?

• A. The sled will go fastest on ice, slower on snow, and slowest on gravel.

• B. The sled will go fastest on gravel, slower on snow, and slowest on ice.

• C. The sled will move at the same speed on all surfaces.

A student rolls a ball across three surfaces: grass, a smooth floor, and a carpet.

On which surface will the ball stop the quickest?

• A. The carpet, because it is rough and slows the ball down.

• B. The smooth floor, because smooth surfaces stop things quickly.

• C. The grass, because it has no effect on the ball.