Edexcel Physics Topic 2: Forces, Motion, and Safety

Comprehensive vocabulary flashcards covering resultant forces, Newton's laws of motion, kinematics, momentum, stopping distances, and vehicle crash safety features based on Edexcel GCSE Physics specifications.

Scalar

A physical quantity that has magnitude (size) only, such as distance, speed, mass, energy, or time.

Vector

A physical quantity that possesses both magnitude (size) and direction, such as displacement, velocity, acceleration, force, weight, or momentum.

Resultant Force

A single force that has the exact same effect on an object as all the individual forces acting on it combined.

Newton's First Law of Motion

The law stating that if the resultant force acting on an object is zero, a stationary object remains stationary and a moving object continues to move at a constant velocity (same speed and straight-line direction).

Centripetal Force

The resultant force acting towards the centre of a circle that maintains circular motion by continuously altering an object's direction and velocity.

Mass

The amount of matter in an object, which is a scalar quantity measured in kilograms ($\text{kg}$) that remains constant anywhere in the universe.

Weight

The force of gravity acting on an object's mass, defined as a vector quantity measured in newtons ($\text{N}$) using the formula $\text{Weight} = \text{mass} \times \text{gravitational field strength}$ ($W = m \times g$).

Newtonmeter

A calibrated spring balance used to measure weight in newtons ($\text{N}$).

Gravitational Field Strength ($g$)

The gravitational force exerted per unit mass, which is approximately $10\,\text{N/kg}$ (or $9.8\,\text{N/kg}$) on Earth.

Newton's Second Law of Motion

The principle stating that an object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass ($F = m \times a$).

Inertial Mass

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

Newton's Third Law of Motion

The law stating that whenever two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction.

Action-Reaction Pair

A pair of forces that are equal in magnitude, opposite in direction, of the exact same type, and acting on two completely separate objects.

Momentum ($p$)

A vector quantity defined as the product of an object's mass and its velocity ($p = m \times v$), measured in kilogram meters per second ($\text{kg}\,\text{m/s}$).

Conservation of Momentum

The principle stating that within a closed system where no external forces act, the total momentum before an event is equal to the total momentum after the event.

Rate of Change of Momentum

The formal definition of resultant force ($F = \frac{mv - mu}{t}$), representing the change in momentum divided by the time taken.

Thinking Distance

The distance travelled by a vehicle during the driver's reaction time, occurring between the moment a hazard is seen and the moment brakes are applied.

Braking Distance

The distance a vehicle travels under the braking force from the moment the brakes are pressed until it comes to a complete stop.

Stopping Distance

The total distance required for a vehicle to come to a halt, calculated as the sum of thinking distance and braking distance.

Reaction Time

The time taken by a person to respond to a hazard, which typically ranges from $0.2\,\text{s}$ to $0.9\,\text{s}$ in humans.

Crumple Zone

A safety feature engineered into the front and rear of a vehicle that intentionally crushes and plastically deforms to lengthen collision time ($t$), reducing the rate of change of momentum and the impact force felt by occupants.

Terminal Velocity

The constant maximum velocity reached by a falling object when the upward resistive force of air resistance balances the downward force of weight, making the resultant force $0\,\text{N}$.

Velocity-Time Graph Gradient

The slope of a velocity-time graph line, which quantifies the acceleration of the object ($a = \frac{v - u}{t}$).

Velocity-Time Graph Area

The geometric area beneath a velocity-time graph line, which equals the total distance travelled by the object.