PHYSICS SAC 1 - Motion

Scalar

Quantities concerned only with magnitude

Examples:

distance - d (m)

speed - s (m/s)

mass - m (kg)

energy - E (J) —> kinetic energy E_k, Gravitational potential E_g

Vector

Quantities that describe both magnitude and direction

Examples:

displacement - s,x (m)

velocity - ν (m/s)

weight - W (N)

force - F (N)

Momentum - ρ (kgm/s)

Distance

A measure of the length of a path taken by an object irrespective of the direction that object is travelling in

Displacement

A measure of change in position of an object taking into account both the distance and the direction from its starting position

*Assign a direction as either positive of negative

Speed

The rate at which an object covers distance (scalar)

Measure: m/s

Velocity

The rate at which an object covers displacement (vector)

Measure: m/s + direction

Speed vs Velocity

They both quantify the rate at which an object moves over time.

Velocity is a vector quantity whilst speed is a scalar quantity.

Velocity is the change in displacement with respect to time, whereas speed is the change in distance travelled with respect to time.

When an object does not change direction, the magnitudes of these two values will be the same, however when it does, they will no longer be equal.

Acceleration

The rate of change of velocity of an object (vector)

Measure: m/s²

**Vector diagrams are useful when calculating the change in velocity to find acceleration

Vector diagram

Change in velcoty: Δv = v-u

where v = final velocity, u = initial velocity

When velocity vectors point in different directions, to subtract take opposite direction of initial velocity

Motion graphs

Velocity time graphs

Calculating distance and displacement

SUVAT

Vertical motion

Forces as vectors

Friction force

Air resistance

The normal force

Force diagrams

Calculating the net force

Newton’s First Law

Newton’s Second Law

Newton’s Third Law

Elevator forces

Inclined planes

Connected bodies

Momentum

Impulse

Torque

Equilibrium