# Physics GCSE, unit one forces and motion

Physics GCSE, unit one forces and motion

HideShow resource information
• Created by: jesper
• Created on: 17-03-12 06:15

## Important terms, Unit 1

Type of forces - What is it?

Push- A force.
Friction- A force that opposes motion.
Normal reaction force - The force that acts in an upwards direction.
Gravitational force/weight- The pull of the earth.
Air resistance- A force taht opposes the movement of objects in air.
Upthrust- An upward push.
Magnetic force- used to make electric motors rotate.
Electrostatic force- To do wit the attractions and repulsions between charges.

1 of 6

## Vector and Scalar

Vector changes in size and direction.

For example:

• Velocity.
• Force.
• Acceleration.
• Momentum.

Scalar only changes in size.

For example:

• Temperature
2 of 6

## Newtons's law of motion

Newton's 1st law
If the forces on an object is balanced – there is no resultant force – the object will either remain at rest or carry on moving at constant speed in a straight line. If the forces on an object is unbalanced, the object will accelerate.

Newton's 2nd law
Resultant force (N) = mass (kg) x acceleration (m/s
2) or F = ma

Newton's 2nd law
For every action there is an equal and opposite reaction.

3 of 6

## Terminal velocity

Terminal velocity is when the upward force is the same as the downward force.

Example

﻿ When a skydiver jumps off the plane, she will accelerate until she reaches terminal velocity. When her parachute opens, it will cause a sudden increase in drag force. This means that there will be an unbalanced force acting upwards, causing her to decelerate. As she slows down, the drag force decreases and a new terminal velocity is reached.

4 of 6

## Thinking distance and Braking distance

Thinking distance= is the time takn for the driver to respond or react
This could be increased if the driver is tired, under the influence of alcohol or drugs/ or poor visability.

Braking distance= is the time takenfor the vehicle to rest after the driver hits the brakes. This could be increased if the road is slipperry or the tyres are screwed up.

5 of 6

## The Turning effect of forces

Moment(Nm)= Force(N) x Perpendicular distance from the pivot(m)

An object will be balanced if:
Sum of anticlockwise moments = sum of clockwise movements

Hooke's law:

load force is directly proportional to extension provided that it is within its elastic limit

6 of 6