# Physics Unit 2

Electricity

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• Created by: Chloe
• Created on: 04-04-11 17:39

## Speed

Speed=how fast an object is moving

Distance-time graphs represent the speed of an object

Velocity=the speed and direction of an object

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## Acceleration

The acceleration or deceleration of an object is the rate at which its velocity changes.

Velocity-time graphs represent the acceleration of an object.

Vf-Vi=Change in Velocity

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## Forces

Forces=pushes or pulls that affect the movement of an object

Resultant force=the sum of all the forces that act on an object

Equal and opposite forces are balanced. Balanced forces keep the movement of an object constant

Unequal and opposite forces are unbalanced. Unbalanced forces change the movement of an object

Terminal Velocity is a steady falling speed, i.e. gravity and are resistance are equal

Stopping Distance= thinking distance + braking distance. Stopping distance can be affected by speed, weather conditions and external factors affecting the car driver or car.

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## Kinetic Energy

Kinetic energy= the energy an object has because of its movement. It depends on the mass and speed od the object

Kinetic energy (J)= 1/2 x Mass (Kg) x Speed^ (m/s)^

Momentum= a measure of the state of motion of an object. It depends on the mass and velocity of the object. Momentum has both magnitude and direction

In a collision or explosion, momentum is conserved providing no external forces act

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## Static Electricity

Static electricity is created when two insulating materials are rubbed against each other

Material minus electrons=positively charged

Material plus electrons=negatively charged

Like charges repel

Different charges attract

Static electricity can be discharged by connecting it to earth with a conductor. Can be used in smoke precipitators and photocopiers

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## Circuits, Current and power

The amount of electricity current that flows through a component depends on...

• Potential difference across component
• Resistance of component

Greater potential difference across a component=greater current through the component

Direct current   flows in the same direction. Alternating current  constantly changes in direction

Circuit breakers and fuses are safety devices designed to break a circuit if the current becomes too high

Electrical energy can be transformed into other types of energy. The rate of this transformation is the power

Charge (coulomb, C) = Current (amp, A) x Time (second, s)

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## Atoms

Atom= protons+neutrons+electrons

Atom has no overall charge

Atomic number=number of protons

Mass number=number of protons and neutrons

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## Nuclear Fission and Fusion

Nuclear fusion=joining of atomic nuclei

Nuclear fission=splitting of atomic nuclei

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