Chapter 1: Forces and Motion Concepts

Force

A force can be a push or a pull.

Contact Force

Contact forces act when two objects are physically touching.

Gravity

Gravity is a non-contact force that acts between two objects.

Newton

A force is measured in Newtons (N).

Air Resistance

Air resistance is an example of a contact force.

Friction

Friction is an example of a contact force.

Gravitational Force

Gravitational force pulls you back to Earth when you jump.

Gravitational Force Dependence

The size of the gravitational force depends on the mass of the two objects and how far apart they are.

Newton Meter

We measure forces with a newton meter.

Non-Contact Force

Non-contact forces act when two objects are physically separated (not touching).

Weight

Weight is the downward force caused by gravity acting upon the mass of an object, it is measured in Newtons (N).

Mass

Mass is the amount of matter within an object, whereas weight is the downward force of the object, we measure mass in kilograms.

Interaction Pairs

Forces always act in pairs, we call these interaction pairs.

Field

We call the region where an object experiences a non-contact force a field, examples of these include gravitational fields and magnetic fields.

Weight Calculation

We calculate weight with the equation: weight (N) = mass (kg) × gravitational field strength (N/kg).

Balanced Forces

When forces acting on an object are the same size, but acting in different directions, we say that they are balanced.

Unbalanced Forces

When the two forces acting on an object are not the same size, we say that the forces are unbalanced.

Speed

Speed is a measure of how quickly or slowly that something is moving.

Distance-Time Graph

Distance-time graphs tell the story of a journey, they show how much distance has been covered in a certain period of time.

Speed Measurement

We measure speed in meters per second (m/s), this means that distance must be in meters and time must be in seconds.

Speed Calculation

We calculate speed with the following formula: speed (m/s) = distance travelled (m) / time taken (s).

Relative Motion

Relative motion compares how quickly one object is moving compared to another.

Resultant Force

The resultant force is the difference between the two unbalanced forces.

Moment

The turning effect of a force, measured in Newton meters.

Moment Calculation

moment (Nm) = force (N) × distance from the pivot (m).

Effect of Friction

The greater the friction, the faster an object will slow down, or the greater the force it will need to overcome the force of friction.

Example of Friction

It is easier to push a block on ice than on concrete, as the ice is smoother and causes less friction.

Increasing Moment Size

The size of the moment will increase as the distance from the pivot or the size of the force increases.

Drag

The force which slows an object moving through a fluid, either liquid or gas.

Effect of Drag

The fluid particles will collide with the moving object and slow it down, meaning that more force is needed to overcome this.

Equilibrium

When an object is balanced, the clockwise and the anticlockwise moments will be equal and opposite.

Pivot

The point about which a moment is calculated.

Seesaw Example

A seesaw is an example of an object that can be in equilibrium when balanced.

Fluid Resistance

The force that opposes the motion of an object through a fluid.

Hooke's Law

A principle stating that the extension of a spring is directly proportional to the force applied to it, until the elastic limit is reached.

Extension

The amount a spring stretches when a force is applied to it.

Stress

The pressure exerted on a solid, defined as force per unit area.

Gas Pressure

The pressure exerted by gas particles colliding with the walls of their container.

Incompressible

A property of liquids indicating that they cannot be compressed significantly.

Linear Relationship

A relationship where doubling one quantity results in doubling another, such as force and extension in Hooke's law.

Atmospheric Pressure

The pressure exerted by the weight of air in the atmosphere, which decreases with altitude.

Elastic Limit

The maximum extent to which a material can be stretched without permanently deforming.

Pressure

The force exerted per unit area.

Newtons (N)

The unit of measurement for force in the International System of Units (SI).

Collisions

Interactions between particles that can affect pressure in gases.

Hydraulic Machines

Devices that use incompressible liquids to transmit force and pressure.