Physics Test A

What are two unwanted effects of friction?

Wear on moving parts and heat production (energy loss).

What is air resistance also called?

Drag.

How can scientists study air resistance?

Using a wind tunnel with smoke lines.

Name two methods of reducing friction.

Using lubricants (oil, grease) and streamlining shapes.

Why do rollerblades use ball bearings?

Rolling friction is less than sliding friction.

How do shark scales reduce drag?

They reduce water turbulence, allowing smoother movement.

Why were polyurethane swimsuits banned?

They trapped air, increased buoyancy, reduced drag, and gave swimmers an unfair advantage.

How does a hovercraft reduce friction?

It rides on a cushion of air.

What are electrical insulators? Give an example.

Materials that don't let electrons flow freely (e.g., plastic, rubber, wood).

What are electrical conductors? Give an example.

Materials that allow electrons to flow (e.g., copper).

What happens when you rub a balloon with a silk cloth?

Electrons transfer from silk to balloon → silk becomes positive, balloon negative.

What is an electric field?

A force field around charged objects that exerts electrostatic force on others.

What happens to objects with like vs. unlike charges?

Like charges repel; unlike charges attract.

What does a Van de Graaff generator do?

Builds up static charge by friction; makes hair stand up due to repulsion.

What is static discharge? Give an example.

Release of built-up charge, e.g., shock from touching a metal door handle.

What causes lightning?

A giant static discharge from a build-up of charge in storm clouds.