Physics Forces Test

Scalar Quantity

A quantity with magnitude (size) but no direction.

Examples of Scalar Quantities

Speed, distance travelled, density, mass, energy, time, power.

Vector Quantity

A quantity with magnitude (size) and direction.

Examples of Vector Quantities

Displacement, velocity, acceleration, force.

How to represent a vector in a diagram

As an arrow; the length represents size and the arrowhead indicates direction.

Weight

The gravitational force acting on an object, always acting downwards.

Centre of Mass

A point around which an object’s mass is equally distributed.

Difference between Mass and Weight

Mass measures how much matter an object has, while weight is the force due to gravity acting on that mass.

What does the weight force depend on?

The gravitational field strength and mass of the object.

Value of g on Earth

g = 9.8 N/kg.

Resultant Force

A single force that has the same effect as all the original forces acting together.

Balanced Forces

When forces cancel out, resulting in zero net force; the object remains at a steady speed or at rest.

Unbalanced Forces

Forces that do not cancel out completely, leading to a change in speed, direction, or shape.

Free Body Diagram

A diagram showing an object as a simplified circle/square with forces represented as labelled arrows.

Tension

The force trying to return an object to its original shape when it is stretched or squashed.

Unit of Force

Newtons.

Upthrust

The force pushing up on objects that are in a fluid, such as a hot air balloon or a boat.

Displacement

The overall distance and direction from a starting point to a finish point, measured in a straight line.

Speed

The distance an object travels in one second, measured in m/s; it is a scalar quantity.

Velocity

The overall speed in a given direction; it is a vector quantity, measured in m/s.

When to use speed = distance/time

When there is a steady speed, with balanced forces and no acceleration.

Acceleration

Rate of change of velocity; it is a vector quantity, measured in m/s².

Steady Speed but Accelerating

An object can be moving at a steady speed while accelerating if it is moving in a circular path.

Finding speed from a distance-time graph

It is the gradient (rise/run) of the graph.

Calculating acceleration from a velocity-time graph

It is the gradient (rise/run) of the graph.

Calculating distance from a velocity-time graph

It is the area underneath the graph.

Newton’s First Law

If there is no resultant force, an object remains at rest or constant velocity.

Drag

The resistive force an object experiences while moving through a fluid; it can be increased by increasing speed or surface area.

Inertia

The tendency of an object to keep its current state of rest or uniform motion.

Newton’s Second Law

Acceleration is proportional to the resultant force and inversely proportional to mass.

Inertial Mass

The ratio of force to acceleration, indicating how difficult it is to change an object's velocity.

Newton’s Third Law

For every action, there is an equal and opposite reaction; forces act on different objects.

Normal Contact Force

The push back force between two objects in contact, always perpendicular to the surface.

Friction

The resistive force between two objects in contact, always acting opposite to motion.

Thrust

The force that pushes an object forwards, typically from an engine or sail.

Elastic Material

A material that returns to its original shape when the deforming force is removed.

Inelastic (Plastic) Material

A material that does not return to its original shape when the deforming force is removed.

Limit of Proportionality

The point on a force-extension graph where a material stops behaving elastically.

Directly Proportional Relationship

When one quantity doubles, the other doubles as well; shown as a straight line through (0,0) on a graph.

Finding spring constant from a force-extension graph

It is the gradient of the graph.

Spring Constant

A measurement of the stiffness of a spring, measured in N/m.