Define a scalar

A quantity that only has magnitude.

Give some examples of scalar quantities

Speed, distance, time, mass, volume

Define a vector quantity

A quantity that has magnitude and direction.

Give some examples of vector quantities

Velocity, displacement, acceleration, momentum, any force

State the difference between distance and displacement

Distance is a scalar - doesn’t involve direction

Displacement is a vector and is measured in a straight line from the start point to the finish point and the direction of that straight line.

State the difference between speed and velocity

Speed is a scalar - only has magniture

Velocity is a vector - has magniture and direction

State some examples of non contact forces

Friction, air resistance, drag, upthrust, tension, normal contact force

State some examples of contact forces

Gravity, magnetism, electrostatic attraction or repulsion

State the equation with all units for Weight

weight (N) = mass (kg) × gravitational field strength(N/kg)

What is the mathematical relationship between weight and mass.

They are directly proportional, if mass doubles then does weight

What equipment can be used to measure weight?

Weight is measured using a calibrated spring-balance called a newtonmeter

Define a resultant force

When a number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together.

Units of force

Newtons (N)

When is work done?

When a force causes an object to move through a distance

What is the relationship between work done and energy transferred

Work done = energy transferred

State the equation and all units for work done

work done (J) = force (N) × distance moved along the line of action of the force (m)

Define 1 joule of work

One joule of work is done when a force of one newton causes a displacement of one metre.

1 joule = 1 newton-metre

State Hooke’s law

The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

State Hookes law equation with all units

force (N) = spring constant (N/m) × extension (m)

When an object is stretched or squared what form of energy does it store?

Elastic potential energy.

Define elastic deformation

When the forces are removed the object returns to its original length

Define inelastic deformation

When the forces are removed the object doesn’t returns to its original length, it stays permanently stretched.

Define a moment

The turning effect of a force

State the equation for a moment, with all units

moment of a force (Nm) = force (N) × perpendicular distance (m)

If an object is balanced what can you say about the clockwise and anticlockwise moments

They must be equal

Define a fluid

Either a liquid or gas, particles must be able to move past each other

State the equation for pressure with all units

pressure = force / area

Pressure - Pa

Force - N

Area - m^{2}

What is the relationship between pressure from a liquid and depth

As depth increases pressure increase due to a greater number of particles and force pushing on the object.

How does liquid pressure cause upthrust?

A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface, (pressure increases with depth).

Force = Pressure x area so there is a greater force on the bottom surface than the top.

This creates a resultant force upwards. This force is called the upthrust.

Define the atmosphere

The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth.

State the relationship between altitude and the density of the atmosphere

he atmosphere gets less dense with increasing altitude.

As altitude increase why does atmospheric pressure decrease?

Air molecules colliding with a surface create atmospheric pressure. The number of air molecules (and so the weight of air) above a surface decreases as the height above ground level increases. So as height increases there is always less air above a surface than there is at a lower height. So atmospheric pressure decreases with an increase in height.

State the equation with all units to calculate speed

distance (m) = speed (m/s) × time (s)

how can speed be calculated from a distance - time graph

Using the gradient

State the equation to calculate average acceleration, with all units

acceleration = change in velocity / time

a = (v-u) / t

acceleration - m/s^{2}

velocity - m/s

time - s

Define acceleration

Rate of change of velocity. An acceleration can be when an object:

- speeds up
- slows down
- changes direction

How can acceleration be found from a velocity - time graph

From the gradient

How can displacement be found from a velocity - time graph

From the area under the line

What is the initial rate of acceleration for an object falling close to the earths surface?

9.8 m/s^{2}

What is terminal velocity and when does it occur?

the maximum velocity an object can fall at, this happens when forces are balanced (Weight = air resistance)

What factors can increase the size of air resistance

- Speed
- Surface area
- Density of the fluid which the object is falling through

State Newtons first law

if the resultant force acting on an object is zero the object will stay at rest or move at a constant velocity

The tendency of objects to continue in their state of rest or of uniform motion is called?

Inertia

State Newtons second law

The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.

a = F/m

State the equation with all units for Newtons Second law

resultant force (N) = mass (kg) × acceleration (m/s2)

Define inertial mass

Inertial mass is a measure of how difficult it is to change the velocity of an object.

Inertial mass is defined as the ratio of force over acceleration.

m = F/a

Define inertia

the tendency of an object to continue in its state of rest or motion

State Newton’s third law

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

Define stopping distance

The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance).

Stopping distance = thinking distance + braking distance

Define thinking distance

the ** distance** the car travels whilst a driver reacts to a situation

Define braking distance

the ** distance** the car travels whilst the brakes are applied

State the typical reaction times for a human

0.2 s to 0.9 s.

State some factors that can affect a persons reaction times

- tiredness,
- ages,
- drugs and alcohol,
- Distractions

State some factors that can affect the braking distance of a car

- Rain,
- ice,
- snow,
- poor quality brakes,
- poor quality tyres,
- gradient of the road,
- mass of the car

State the one factor that can increase both the thinking distance and braking distance

Speed

State the equation for momentum

momentum (kgm/s) = mass (kg) × velocity (m/s)

State the units for momentum

kg m/s

Define the conservation of momentum

In a closed system, the total momentum before an event is equal to the total momentum after the event.

Provided no external force is applied

What is required to change the momentum of an object

A force

Explain safety features such as: air bags, seat belts, gymnasium crash mats, cycle helmets and cushioned surfaces for playgrounds with reference to the concept of rate of change of momentum.

An air bag increases the ** time** for a person to stop. Therefore for the **same change of momentum** a **smaller force** can be used.

Force = change in momentum/time

What is the centre of mass of an object?

The point at which the mass may be thought to be concentrated

Where does the centre of mass lie in symmetrical objects?

Along the line of symmetry

How can the centre of mass of an irregular shape be found?

by hanging the shape from a point and a plumb line is used to draw a vertical line downwards from the pivot. this is repeated from different points Where the lines meet is the centre of mass

What is a gear?

A rotating machine with cogs that mesh with another toothed part to transmit a moment

What do gears act as?

A force multiplier

What are the dangers of a large braking force?

Brakes overheating, loss of control and skidding

State the typical walking speed of a person

1.5 m/s

State the typical running speed of a person

3.0 m/s

State the typical cycling speed of a person

State the speed of sound

330 m/s