P2 Forces and Motion Concepts

Distance

Can be measured in mm, cm, m and km.

Time

Is measured in ms, s, mins and hours.

Speed

Calculated using the formula speed = distance / time.

Vector

Has magnitude and direction.

Scalar

Has just magnitude and generally cannot be negative.

Velocity

A vector that gives speed in a given direction.

Distance-Time Graphs

Typically have time on the x-axis and distance on the y-axis; the gradient shows velocity.

Gradient

The steeper the gradient, the faster the speed.

Negative Gradient

Indicates the moving object is returning back to the starting point.

Horizontal Line

Indicates the object is stationary.

Curved Line

Indicates the velocity is changing and the object is accelerating or decelerating.

Velocity-Time Graphs

Typically have time on the x-axis and velocity on the y-axis; the gradient shows acceleration.

Average Speed

Calculated using the formula average speed = total distance / total time.

Electrostatic Interaction

Occurs between charged particles, where they experience a force of attraction or repulsion.

Gravitational Attraction

Occurs between particles with mass.

Contact Forces

Experienced in the opposite direction to contact, such as friction.

Free Body Force Diagrams

Show the direction of forces that are present on an object in a situation.

Reaction Force

Always acts normal (perpendicular) to the line of contact, from the point of contact.

Friction

Acts in the opposite direction to movement, along the line of contact.

Weight

Always acts vertically downwards, acting from the object's centre of mass.

Scale Drawings

The length of each arrow represents its size in relation to the other forces acting on the object.

Resultant Force

The larger arrow shows the resultant force.

Equilibrium

Occurs when forces cancel out so the object travels at a constant velocity.

Newton's First Law

An object has a constant velocity unless acted on by a resultant force. If a resultant force acts, the object will accelerate.

Acceleration

Change in velocity over time, affecting the direction and/or speed of the object.

Terminal Velocity

The speed at which the thrust is balanced by drag and friction, resulting in no resultant force and no further acceleration.

Newton's Second Law

The acceleration or deceleration experienced depends on the direction and magnitude of the resultant force.

Force Equation

F = m × a, where F is force, m is mass, and a is acceleration.

Inertia

The measure of how difficult it is to change the velocity of an object depending on its mass.

Momentum

The product of an object's mass and velocity, defined as p = m × v (units Ns or kg·m/s).

Elastic Collision

In an elastic collision, both momentum and kinetic energy are conserved.

Work Done

Work is done when energy is transferred from the object doing the work to another form, calculated as W = F × d.

Distance in Work Done

Distance is the distance moved along the line of action of the force.

Work Done Measurement

Work done is measured in Joules.

Deformation

Changes in shape caused by stretching forces, also called distortion.

Elastic Deformation

The object returns to its original shape when the load has been removed.

Plastic Deformation

The object does not return to its original shape when the load has been removed.

Example of Work Done

If a book is lifted 1m in the air, work is done against gravity, transferring energy from muscles to the book.

Example of Reaction Force

The weight of a book on a table is equal to the reaction support force on the book by the table.

Example of Rocket Lift

The force of the gases being ejected from the rocket is equal to the force that lifts the rocket from the surface.

Single Force Application

If a single force is applied to an object, it will just move in that direction.

Multiple Force Application

To stretch, bend or compress an object, more than one force has to be applied.

Stretching Object

If pulled in opposite directions on either side of the object, the object will stretch.

Fixed Point Force

If fixed at one point and pulled from another point, a force is still being applied by the fixed point.

Gun and Bullet Example

A stationary gun of 10kg loaded with a bullet is fired, demonstrating momentum conservation.

Hooke's Law

F = kx, where F is the force applied to the spring (N), k is the spring constant (N m−1), and x is the extension (m).

Elastic Limit

The point at which the trend stops being linear on a Force-Extension graph, after which it does not obey Hooke's Law.

Non-Linear Lines

Lines that show non-elastic behaviour and do not obey Hooke's Law.

Brittle Material

A material that is linear with no non-linear end section and will snap instead of stretching after the elastic limit.

Work Done on a Spring

Calculated as the area under the force-extension graph: W = (1/2)kx^2.

Gravitational Field Strength

The strength of the gravitational field, affecting the weight of an object based on its mass.

Acceleration in Free Fall

Due to gravity, it is the same as g (9.81 m s−2).

Gravitational Potential Energy

Calculated as PE = mass × field strength × height.

Moment of a Force

Calculated as M = force × perpendicular distance from the pivot.

Gears

Can change speed, force, or direction by rotation.

Lower Gear

Has fewer teeth and will turn faster as less force is applied in the opposing direction.

Higher Gear

Has more teeth and will turn slower as a greater force is applied in the opposing direction.

Pressure in Fluids

Causes a net force at right angles to any surface.

Pressure Formula

Pressure (p) = force / area (to the normal).

Bed of Nails vs. Single Nail

On a bed of nails, the force is spread out over a larger area, reducing pressure; on a single nail, the area is small, increasing pressure.

Hydraulic Brakes

A piston forced into a narrow cylinder connected to wider cylinders multiplies the force applied, creating greater braking force due to constant pressure in fluids.