Chapter 3: Motion and Pressure

Vocabulary flashcards covering motion, speed, moments, and pressure in solids, liquids, and gases based on the Chapter 3 knowledge organiser.

Speed

How far something moves in a certain time, measured in metres per second ($m/s$).

Relative motion

A comparison of how fast one object is moving to another; it is zero if two objects move at the same speed in the same direction.

Distance-time graph

A graph showing the distance something travels over a certain time, used to calculate average speed by dividing distance covered by time taken.

Moment

The turning effect of a force, measured in newton metres ($Nm$).

Law of moments

The principle that when forces are balanced, all clockwise moments added together must equal all anticlockwise moments added together.

Centre of gravity

The point through which all the weight of an object seems to act; it is also known as the centre of mass.

Gas pressure

The pressure produced by collisions between gas particles and their container.

Compress

To squash a gas into a smaller volume, which results in more collisions and higher pressure.

Atmospheric pressure

The pressure acting on us from the air around us, which is lower at higher altitudes because the air is less dense.

Pressure (in solids)

The force exerted on a surface because of weight, measured in newtons per metre squared ($N/m^2$) or Pascal ($Pa$).

Pascal ($Pa$)

A unit of pressure where $1\,N/m^2 = 1\,Pa$.

Incompressible

The property of solids and liquids where particles are already touching, meaning they cannot be squashed and instead pass pressure on.

Liquid pressure

Pressure in a liquid that is bigger at the bottom than the top because the weight of the water pushing down increases with depth.

Upthrust

The upward force produced by liquid water pressure that allows objects to float.

Pivot

The point around which a moment or turning force acts.

Newton metres ($Nm$)

The unit for the moment, calculated as $\text{force (N)} \times \text{perpendicular distance from the pivot (m)}$.