# GCSE Physics Energy and Force

These are some of my class notes that I find useful so please rate and comment so i may make them better. Thanks! ^_^

- Created by: Dale McNerlin
- Created on: 12-04-11 10:02

## Types of Energy

- 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.

## Formula for Kinetic Energy

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

## How do I find the Velocity?

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

## How to find the mass

## Work Done

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. Part 1

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

## Electrical Power. Part 2

W = J / S

E = Energy (J)

P = Power (W)

T = Time (S)

P = Energy / Time

T = Energy / Power

E = Power x Time

## Centipetal Acceleration

## Cetripetal Acceleration (Explained)

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.

## Formulas For Centripetal Acceleration

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)

## Forces

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.

## Acceleration

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)

## Newtons First Law (Inertia)

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)

## Newtons Second Law

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

## Free Fall Part 1

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

## Free Fall Part 2

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.

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