Forces

Flashcards covering key definitions, laws, and equations from AQA GCSE Physics Topic 5: Forces, including vectors, scalars, Newton's Laws, momentum, and pressure.

Vector

A quantity that has both magnitude and direction.

Scalar

A quantity that has magnitude only.

Non-Contact Force

A force where the interacting objects are physically separated, such as electrostatic or gravitational attraction.

Contact Force

A force where the interacting objects are physically touching, such as friction or normal contact force.

Weight

The force exerted on a mass by a gravitational field, calculated as $W = mg$, where $g \times 9.8\,N/kg$ on Earth.

Centre of mass

The specific point at which the weight of an object is considered to act.

Resultant Force

A single force representing the sum of all the forces acting on an object.

Terminal velocity

The constant speed reached by a falling object when the resultant force is $0$ because air resistance equals weight.

Work Done

The energy transferred when a force causes an object to move, calculated using $W = Fs$ where $s$ is distance in the line of action of the force.

Joule

The unit of work where $1\,joule = 1\,newton-metre$, occurring when a force of one newton causes a displacement of one metre.

Elastic Deformation

A change in shape where the object returns to its original form once the load is removed.

Plastic Deformation

A change in shape where the object does not return to its original form after the load is removed.

Hooke’s Law

The principle stating that the extension of an elastic object is directly proportional to the force applied, provided the limit of proportionality is not exceeded ($F = kx$).

Spring Constant ($k$)

The gradient of the linear region on a Force/Extension graph, measured in $Nm^{-1}$, representing the stiffness of the spring.

Moment of a Force

The turning effect of a force, calculated as $M = Fd$, where $d$ is the perpendicular distance from the pivot to the line of action of the force.

Equilibrium

A state reached when the sum of anticlockwise moments is equal to the sum of clockwise moments.

Pressure

The force exerted per unit area, calculated as $p = \frac{F}{A}$ and measured in pascals ($Pa$).

Upthrust

A resultant upwards force on a submerged object caused by the pressure on the bottom surface being greater than the pressure on the top surface.

Buoyancy force

The upwards force that counteracts the weight of a floating object, equal to the weight of the fluid displaced.

Displacement

A vector quantity measuring the distance an object moves in a straight line from the start point to the finish point including the direction.

Velocity

A vector quantity defined as speed in a given direction.

Acceleration

The rate of change of velocity, calculated as $a = \frac{v - u}{t}$.

Newton’s First Law

An object remains at constant velocity (stationary or moving) unless acted on by a resultant force.

Inertia

The tendency for objects to continue in uniform velocity or stay at rest.

Newton’s Second Law

The acceleration of an object is proportional to the resultant force and inversely proportional to the mass ($F = ma$).

Inertial mass

A measure of how difficult it is to change the velocity of an object, defined as the ratio of force over acceleration ($m = \frac{f}{a}$).

Newton’s Third Law

Whenever two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction.

Stopping Distance

The total distance traveled after a hazard is seen, equal to the sum of thinking distance and braking distance.

Momentum

The product of an object's mass and velocity, calculated as $p = mv$ and measured in $kgms^{-1}$; it is conserved in closed systems.

Crumple zones

Safety features at the front of a car that deform upon impact to increase the time taken to stop, thereby reducing the rate of change of momentum and the force on passengers.