KS3 Science Unit 3 Revision

Define balanced force

Define balanced force

forces that are equal in size but opposite in direction

Define unbalanced force

Forces that cause a change in the motion (speed and/or direction) of an object

Describe the change in movement caused by balanced force

No change in movement

Describe the forces that cause an object to increase or decreases in speed

forces are opposite in direction but not equal in sizes

Describe the forces that cause an object to change direction

forces may be equal in sizes but are not opposite in direction

State the standard unit for speed

metres per second

State the equation for speed

speed = distance/time

Sketch a distance-time graph

Define lever

a bar that is free to turn about a fixed point

Define pivot

A point around which something can rotate or turn.

Define moment

The turning effect of a force

State the equation for moment

moment = force x perpendicular distance from pivot

State the unit for moment

Newton metre (Nm)

Describe the factors that affects the moment of a force

1. Size of force (the bigger the force, the bigger the moment).
2. The distance between the point acting force and the pivot (the greater the distance, the greater the moment)

Define pressure

the result of a force, exerted by a substance, distributed over an area

State the equation for pressure in solid

pressure = force/area

State the unit of pressure

Newtons per metre squared (N/m²)

Describe how size of force affects pressure

As the force increases, the pressure increases.

Describe how surface area affects pressure

As the surface area decreases, the pressure increases.

Explain pressures in gases and liquids using particle theory

Particles move randomly, and collide with the walls of the container. Each collision exerts a small force on the wall, the area where the collision happened, which causes pressure.

Explain how increasing the amount of fluids (liquid and gas) affects pressure

As the amount of fluids increases, the amount of particles in the container increases, so the collisions with the wall also increases.

Explain how depth affects pressure in fluids (liquid and gas)

As the depth deepen, the pressure increases.
The deeper in a fluid, there are more particles above, so there is more weight (force) that pushes on the particles.

Explain how height affects the atmospheric pressure

As the altitude increases, the atmospheric pressure decreases.
The higher in the atmosphere, the concentration of particles decreases, as most particles are pulled towards the surface by gravity; the weight of the air particles above the current position decreases

Explain how temperature affects pressure in fluids (liquid and gas)

As temperature increases, the pressure increases.
When temperature increases, the particles move faster. The particles collide with the wall more frequently and their collisions exert more force.

Explain why there is no pressure in a vacuum

There are no particles to collide in vacuum.

Define diffusion

The movement of particles from an area of high concentration to an area of low concentration.