Detailed Notes: 4. Mechanics and Materials: Paper 1: Physics A Level AQA

This should be used when vectors are at angles other than 90°.

Scale Drawing

Moment

The moment of a force about a point is the force multiplied by the perpendicular distance from the line of action of the force to the point.

Couple

A couple is a pair of coplanar forces (meaning they are forces within the same plane), where the two forces are equal in magnitude but act in opposite directions.

Speed

This is a scalar quantity which describes how quickly an object is travelling.

Displacement (s)

The overall distance travelled from the starting position (includes a direction as it is a vector quantity).

Instantaneous velocity

Instantaneous velocity is the velocity of an object at a specific point in time. It can be found from a displacement-time graph by drawing a tangent to the graph at the specific time and calculating the gradient.

Average velocity

Average velocity is the velocity of an object over a specified time frame. It can be found by dividing the final displacement by the time taken.

Free fall

Free fall is where an object experiences an acceleration of g.

Friction

Friction is a force which opposes the motion of an object, and it is also known as drag or air resistance when considering friction experienced in a fluid. Frictional forces convert kinetic energy into other forms such as heat and sound.

Newton’s 1st law

Newton’s 1st law - An object will remain at rest or travelling at a constant velocity, until it experiences a resultant force.

Newton’s 2nd law

Newton’s 2nd law - The acceleration of an object is proportional to the resultant force experienced by the object: F = ma where F is the resultant force, m is the object’s mass and a is its acceleration.

Newton’s 3rd law

Newton’s 3rd law - For each force experienced by an object, the object exerts an equal and opposite force.

Momentum

Momentum is the product of mass and velocity of an object.

Elastic

Elastic - where both momentum and kinetic energy are conserved.

Inelastic

Inelastic - where only momentum is conserved, while some of the kinetic energy is converted into other forms (e.g heat, sound, gravitational potential) and may be larger or smaller after a collision

Work done (W)

Work done (W) is defined as the force causing a motion multiplied by the distance travelled in the direction of the force.

Efficiency

Efficiency is a measure of how efficiently a system transfers energy. It is calculated by dividing the useful power output by total energy input.

Limit of proportionality (P)

The limit of proportionality (P) is the point after which Hooke’s law is no longer obeyed.

Tensile stress

Tensile stress - Force applied per unit cross-sectional area.

Tensile strain

Tensile strain - This is caused by tensile stress, and is defined as the extension over the original length.

Breaking stress

Breaking stress is the value of stress at which the material will break apart, this value will depend

on the conditions of the material e.g its temperature.

Plastic

Plastic - This is where a material will experience a large amount of extension as the load is

increased, especially beyond the elastic limit.

Brittle

Brittle - This is where a material will extend very little, and therefore is likely to fracture (break apart) at a low extension.

Young modulus

The Young modulus is a value which describes the stiffness of a material.