Physics 2
Atoms

Have a nucleus containing protons and neutrons

Electrons surround the nucleus

Atom has no overall charge
Electrostatic charges
Electrostatic charges:
Insulating materials can be given an electrostatic charge by rubbing two materials together.
Electrons are transferred from one material to another.
The material that has gained electrons has a negative charge and the other a positive charge.
A charged object can attract uncharged objects, it induces a charge on the object.
Uses and Dangers
Uses and Dangers
Electrons can move to cancel out a charge on you, maybe cause a ‘shock’. This is called earthing.
Lightning happens when a charge builds up in clouds.
Using static electricity:
Used in paint sprayers. Droplets all get the same kind of charge so they repel and spray evenly and attracts to the object of opposite charge.
A bonding line has to be used to earth any static charge on an aeroplane or truck before refuelling starts.
Electric Currents
Electric Currents
The size of a current is a measure of how much charge flows past a point each second, the rate of flow of charged particles.
Measured in coulombs(C).
One amp is one C of charge per second.
Charge = current × time
Q = I × T
Key points:

Conductors are difficult to charge because the electrons can easily move through them

A flow of electrons is an electric current
Current and Voltage
Current and Voltage
The current in a circuit is measured using an ammeter.
The voltage is measured using a voltmeter.
1 volt = 1 joule per coulomn
If the voltage is increased, the current increases, if it is decreased, the current decreases.
Resistance, Current and voltage
Resistance, Current and voltage
Resistance is a way of measuring how hard it is for electricity to flow through it.
Measured in ohms(Ω).
Higher the resistance, smaller the current.
A resistors or variable resistors can change the resistance.
Calculations:
Potential difference/voltage(volts) = current(amps) × resistance(ohms)
V = I × R
Shorter wire = less resistance = more current = brighter bulb
Transferring Energy
Transferring Energy
Power:
Power is the energy per second
Measured in Watts
1 Watt = 1 Joule per second

Electrical power(watt) = current(amp) × potential difference/voltage(volt)
P = I × V
P = V^{2}/R
P= I^{2}R
Energy
Energy:
Total energy transferred by an appliance depends on its power and how longs its switched on

Energy transferred(joule) = current(amp) × potential difference/voltage(volts) × time(seconds)
E = I × V × t
Must be converted to seconds.
Vectors and Velocity
Vectors and Velocity
Vectors have both size and direction.
Distance – path/route taken

Displacement – distance in a straight line from start to finish
Distancetime graphs:

Gradient = speed

Speed is always positive

Velocity can be positive or negative
Velocity(m/s) =
Velocity and Acceleration
Velocity and Acceleration
Acceleration:

Is a change in velocity

Is a vector quantity
Acceleration(m/s^{2}) =
a =
a = acceleration
v = final velocity
u = initial velocity
t = time taken
Velocitytime graphs
Velocitytime graphs:

The area under the graph represents the distance travelled by the object
Resultant Forces
Resultant Forces
If there is more than one force on something, all the forces can be combined into a resultant force.
Freebody diagrams:

Shows all the forces on something

Shows the direction

Larger forces shown using longer arrows

Used for forces on the same body
Action and reaction forces:

Two touching objects exert force onto each other
Forces and Acceleration
Forces and Acceleration
Acceleration depends on 2 things:

Mass of the object

Size of the force
Force(N) = mass(kg) × acceleration(m/s^{2})
Terminal Velocity
Terminal Velocity
Calculating weight:

The gravitational field strength on Earth is 10N

Mass must always be in kilograms
Weight(N) = mass(kg) × gravitational field strength(N/kg)
W = m × g

Mass – quantity of matter (doesn’t change)

Weight – measure of the pull of gravity on an object (can change)
Terminal Velocity:
Terminal Velocity:

The force of gravity on a large mass is more than on a smaller mass

But the large mass also needs a greater force to accelerate it

The two affects cancel out

All masses fall at the same rate in a vacuum

The acceleration due to gravity on Earth is 10 m/s^{2}
Gravity has units of acceleration too. It is not a force, but acts on objects to cause downwards acceleration.
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