GCSE Physics Energy and Force

• Light
• Sound
• Kinetic Energy
• Heat/Thermal
• Nuclear Energy
• Gravitational Potential Energy
• Electrical
• Elastic Potential Energy
• Chemical

These may come up in your test wheter its multiple choice or just a normal written exam.

Kinetic Energy (J) = 1/2 x mass x (Velocity(m/s)²

KE= 1/2mv²

For Example 

mass = 12                           Velocity = 2

KE=1/2 x 12 x 2²

KE= 6 x 4

KE = 24

As the velocity and mass are in this formula it is possible to find them from the formula

 (I couldnt make thid using  the keyboard)

K = 10

m = 5

V = (Square root) of 2 x 10 / 5 = 4

V = (Square root of 4) = 2

    This is the formula to find mass from Kinetic Energy

For Example

K= 2           V= 4

m = 2 x 2 (divide) 4²

4 (divide) 16

M = 4

When any object is moved around (pushed or pulled) work will need to be done on it to get it to move.

We can work out the amount of work done in moving an object using the formula.

Work done (J) = Force (N) x Distance moved (M)

Work Done is a change in energy one form of energy changing into another.

Electrical Power = Voltage x Current

P=V x I             Power also tells you how quickly you are using energy.

P =  Power. The units ofr power are Watts (W)

V = Voltage.The units for this is Volts (V)

I = Current. The units are Amps (A)

I = P / V

V= P / I

1 Watt = 1 Joule per second

W = J / S

E = Energy (J)

P = Power (W)

T = Time (S)

P = Energy / Time

T = Energy / Power

E = Power x Time

An Object moving in a circular path has a constant speed and a changing velocity due to the direction of motion always changing.

Achanging velocity produces an acceleration called centripetal acceleration.

This acceleration is always directed towards the centre of the object

To create centripetal acceleration you need a constant force

This is called a centripetal force.

It is also directed towards the centre  of the rotating object.

ac = v² / r                                                                Force is increased if you;

fc = m x v² / r                                                    Increase the mass of the object

m = mass                                                         Increase the Velocity

V = velocity                                                      or decrease the radius of the circle

r = radius                                                         or other example of centripetal force are

ac = Centripetal Acceleration                            Orbits (of planets or Moons)

fc = Centripetal Force                                      Electrons (electron movement)

Vectors / Scaler

Vectors and scalers are used to describe different measured quantities in physics.

A Scaler Quantity : has an amount (or Magnitude) but no direction.

Distance, Speed, Time, Massare all examples of scaler (energy and power are other examples)

A Vector Quantity has both a magnitude and a direction.

Displacement, Velocity, Acceleration, Force, Weight are all vector quantities.

D-T graphs describe velocity

V-T graphs describe acceleration (Gradient) and DIstance.

a= v - u / t

a = m/s² metres per second

v = final speed (m/s)

u = Initial speed (m/s)

t = time (s)

Inertia (balanced forces)

Inertia is related to mass and is a objects ability to resist a change in motion.

If the forces are equal (balance):

1) If an object is at rest, it wil remain at rest.

2) If an object is moving, it will keep on moving in a straight line, at a constant speed.

Resultant force is the sum of all the forces acting on an object.

Example - Fr = 100N (Thrust) - 100N (Friction)

This explains what happens with Unbalanced force.

Weight = Reaction force (balanced)

Thrust > friction (Unbalanced)

An Unbalanced force causes an acceleration or deceleration.

F = MA

F- Resultant force (N)          m = mass (Kg)       A = Acceleration (m/s²)

a = v / t                   a = f / m                   m = f /a  

In free fall objects fall at a specifica acceleration, which is due to gravity.

This acceleration is 9.81 m/s²

It will continue to accelerate until it reaches terminal velocity.

Terminal Velocity is the point when the force of gravity (pulling the object down) and the force of friction (pushing upwards) are balanced.

When these forces are balanced, there is no acceleration and the object falls at a constant speed. For a skydiver, this is about 135 mph (216 km/h or 60 m/s)

1) Initial jump - only force on the person is weight (force due to gravity) Acceleration = 9.81 m/s². Velocity = Rapidly increasing

2) In free fall weight stays the same but air resistance (Fair) begins to increase. Acceleration is slowing (less than 9.81 m/s²) and speed is slowly increasing.