GCSE PHYSICS: UNIT 2-FORCES, SPACE AND RADIOACTIVITY

Key Definitions and Common Questions

How do you calculate stopping distance?

Thinking Distance + Braking Distance

What is thinking distance?

The distance a car travels when the driver is reacting.

What is braking distance?

The distance a car travels after the brakes have been applied.

What factors affect thinking distance?

Alcohol; Drugs; Tiredness.

What factors affect braking distance?

Worn brakes/tyres; Icy/wet roads.

Which factor affects both thinking and braking distance?

Speed (hence speed limits).

What is Newton's 1st law?

An object will remain at rest or in uniform motion in a straight line unless acted upon by an external resultant force.

What is inertia?

Inertia is a resistance to a change in motion.

What is Newton's 2nd law?

resultant force = mass x acceleration or F = ma

What is weight?

Weight is the force of gravity acting on an object.

What is mass?

Mass is the amount of matter in an object.

How is terminal speed attained?

Air resistance / drag increases when a body accelerates - until the forces are balanced (or until it equals the weight/thrust).

What is Newton's 3rd law?

If a body A exerts a force on body B then body B exerts an equal and opposite force on body A.

How does a rocket take off?

The rocket pushes exhaust gases down; the exhaust gases push the rocket up.

What happens to a rocket's acceleration through its journey?

The acceleration increases as it goes up because its weight decreases, which increases the resultant force.

Describe how the energy efficiency of vehicles is improved.

Aerodynamic losses are reduced by more streamlined designs. Rolling resistance is reduced by having correctly inflated tyres and using materials which don't heat up as much as they are squashed. Stop-start systems reduce idling losses. Inertial losses are reduced by having lighter cars.

What are the common safety features in a car?

Seat belts; Airbags; Crumple Zone.

How do the safety features protect the driver/passengers?

An air bag and a crumple zone increase the distance over which the energy is transferred, so reducing the force. The same change in momentum happens over a longer time so there is decreased deceleration so the force decreases.

What is work done?

Work is a measure of the energy transfer.

What is kinetic energy?

A body's energy by virtue of its motion.

What is gravitational potential energy?

A body's energy by virtue of its position.

What is Newton's 2nd Law in terms of momentum?

Force = change in momentum / time