P2.2 The Kinetic eNERGY

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  • Created on: 28-04-13 13:08
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P2.2 The kinetic energy of objects speeding up or slowing down
P2.2.1 Forces and Energy
When a force causes an object to move through a distance work is done.
W=F x d
W is the work done in joules: J
F is the force applied in Newton: N
d is the distance moved in the direction of the force in metres: m
Energy is transferred when work is done work done is against frictional forces.
Power is the work done or energy transferred in a given time:
P= E/T
Pthe power in watts: W Ethe energy transferred in joules: J tthe time taken in
seconds: s
Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational
field.
Ep = m x g x h
Ep is the change in gravitational potential energy in joules, J
m is the mass in kilograms, kg
g is the gravitational field strength in Newton per kilogram, N/kg
h is the change in height in metres, m
The kinetic energy of an object depends on its mass and its speed.
Ek = ½ (0.5) x m x v2
Ek is the kinetic energy in joules, J
m is the mass in kilograms, kg
v is the speed in metres per second, m/s
P2.2.2 Momentum
Momentum is a property of moving objects.
P= m x v
p is momentum in kilograms metres per second, kg m/s
m is the mass in kilograms, kg
v is the velocity in metres per second, m/s
In a closed system the total momentum before an event is equal to the total momentum after the event.
This is called conservation of momentum.
P2.3 Currents in electrical circuits
The current in an electric circuit depends on the resistance of the components and the supply.
P2.3.1 Static electricity
When certain insulating materials are rubbed against each other they become electrically charged.
Negatively charged electrons are rubbed off one material and onto the other. The material that gains
electrons becomes negatively charged. The material that loses electrons is left with an equal positive
charge. When two electrically charged objects are brought together they exert a force on each other.
Two objects that carry the same type of charge repel. Two objects that carry different types of charge
attract. Electrical charges can move easily through some substances, for example metals.
P2.3.2 Electrical Circuits
Electric current is a flow of electric charge. The size of the electric current is the rate of flow of electric
charge.
I = Q/t
I is the current in amperes (amps), A
Q is the charge in coulombs, C
t is the time in seconds, s

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P2.2 The kinetic energy of objects speeding up or slowing down
The potential difference (voltage) between two points in an electric circuit is the work done (energy
transferred) per coulomb of charge that passes between the points.…read more

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P2.2 The kinetic energy of objects speeding up or slowing down
Cells and batteries supply current that always passes in the same direction. This is called direct current
(d.c.). An alternating current (a.c.) is one that is constantly changing direction. Mains electricity is an a.c.
supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V. Most electrical
appliances are connected to the mains using cable and a threepin plug.…read more

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P2.2 The kinetic energy of objects speeding up or slowing down
The basic structure of an atom is a small central nucleus composed of protons and neutrons surrounded
by electrons. Atoms may lose or gain electrons to form charged particles called ions. The
atoms of an element always have the same number of protons, but have a different number of neutrons
for each isotope. The total number of protons in an atom is called its atomic number.…read more

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