1) Speeding up and Slowing Down

2) Motion

3) Work, Energy and Momentum

4) Static Electricity

5) Current Electricity

6) Mains Electricity

7) Nuclear Physics

• Created by: Jennifer
• Created on: 13-04-11 15:32

## Speeding up and slowing down

Forces Between objects

- When two objects interact, they always exert equal and opposite forces on each other

- Force is measured in Newtons

Resultant force

- Object at rest = 0 resulant force = stays at rest

- Moving = 0 rf = Velocity stays the same

- Moving = non-zero in the same direction as the direction of motion of the object = accelerates

- Moving = non-zero in the opposite direction to the direction of motion of the object = deccelerates

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## Speeding up and Slowing down

Force and Acceleration

- Resultant force (N) = mass (kg) x acceleration (m/s squared)

- Thinking Distance = distance travelled during the time it takes for the driver to react

- Braking Distance = the distance between reacting and actually stopping

- Stopping Distance = Thinking distance + braking Distance

Falling Objects

- The weight of an object is the force of gravity on it

- An object falling freely accelerates at about 10m/s(2)

- An object falling in a fluid reaches a terminal velocity

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## Motion

Distance-Time graphs

- the steeper the gradient on a distance-time graph, the greater the speed it represents

- Speed (m/s) = Distance (m) / Time (s)

Velocity and acceleration

- Velocity is the speed in a given direction

- Acceleration is change of velocity per second

- A body travelling at a steady speed is accelerating if its direction is changing

Velocity-Time graphs

- The slope of the line on a velocity-time graph represents acceleration

- The area under the line represents distance travelled.

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## Motion

Graphs - Overview

- The slope on a distance-time graph = speed

- The slope on a velocity-time graph = acceleration

- The area under the line on a velocity- time graph = the distance travelled

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## Work, Energy and Momentum

Energy and Work

- Work Done = Energy Transformed

- Work Done (J) = Force (N) x distance moved in the direction of the force (m)

Kinetic Energy

- Elastic Potential energy is the energy stored in an elastic object when work is done on the object

- The Kinetic Energy of a moving object depends on its mass and its speed

- Kinetic Energy = 0.5 x mass (kg) x speed2 (m/s)

Momentum

- Momentum (kg m/s) = mass (kg) x velocity (m/s)

- Momentum is conserved whenever objects interact, provided no external forces act on them.

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## Work, Energy and Momentum

Collisions and Explosions

- Momentum has size and direction

- When two objects push each other apart, they move apart with equal and opposite momentum

Changing Momentum

- The more time and impact takes, the less the force exerted

- Force (N) = change of momentum (kg m/s) / time taken (s)

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## Static Electricity

Electrical Charges

- Like Charges repel (**/NN), unlike charges attract (NS/SN)

- Insulating materials that lose electrons when rubbed become positively charged

- Insulating Materials that gain electrons when rubed become negatively charged

Charge on the move

- Electrical current is the rate of flow of charge

- A metal object can only hold charge if it is isolated from the ground

- A metal object is earthed by connecting it to the ground

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## Current Electricity

Resistance

- Resistance (ohms) = potential difference (volts) / current (amps)

- The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor

Series Circuit

- for components in series a) the current is the same in each component, b) the potential differences add to give the total potential difference, c) the resistances add to give the toal resistance

Paralllel Circuits

- for components in parallel a) the potential difference is the same across each component, b) the total current is the sum of the currents through each component c) the bigger the resistance of a component, the smaller its current is.

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## Mains Electricity

Alternating Current

- Alternating current repeatedly reverses its direction

- Mains electricity is an alternating current supply

- A mains circuit has a live wire which is alternately positive and negative every cycle and neutral wire at zero volts

Cables and Plugs

- Cables consist of two or three insulated copper wires surrounded by an outer layer if flexible plastic material

- Sockets and plugs are made of stiff plastic materials which enclose the electrical connections

- In a three-pin plug the live wire is Brown (Bottom Right), the neutral wire is Blue (Bottom Left) the earth wire is yellow green (top)

- The earth wire is used to earth the metal case of a mains appliance

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## Mains Electricity

Fuses

- A fuse contains a thin wire that heats up and melts, cutting the current off, if too much current passes through it

- A circuit breaker is an electromagnetic switch that opens and cuts the current off if too much current passes through it

Electrical Power and potential difference

- The power supplied to a device is the energy transfer to it each second

- Electrical Power supplied (watts) = current (amps) x potential difference (volts)

Electrical energy and charge

- Charge (coulombs) = current (amps) x time (s)

- Energy transferred (j) = potential difference (v) x charge flow (coulombs)

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## Nuclear Physics

Discovery of the Nucleas

- Alpha particles in a beam are sometimes scattered through large angles when they are directed at a thin metal foil

Nuclear Fission

- Nuclear Fission occurs when a uranium-235 nucleus or a plutonium-239 nucleus splits

- A chain reaction occurs in a nuclear reactor when each fission event causes further events

- In a nuclear reactor, one neutron per fission on average goes on to produce further fission

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## Nuclear Fusion

Nuclear fusion

- Nuclear Fusion occurs when two nuclei are forced close enough together so they from a single larger nucleus

- Energy is released when two light nuclei are fused together

- A fusion reactor needs to be at a very high temperature before nuclear fusion can take place.

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