# Physics two

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• Created by: amy
• Created on: 19-05-16 21:24
• Physics two
• Forces
• Laws
• If an object is not moving and it has no force on it, it will be stationary
• The force pushing a grounded object up is called the normal
• When a force acts on a stationary object the object moves in the direction of the force
• If no force is acting on a moving object it doesnt stop.
• Acceleration
• Acceleration is the rate of change in velocity. This means an object only accelerates if:
• Its speed changes
• Its direction changes
• Terminal velocity
• No motion doesnt mean no force
• Constant speed means no resultant speed
• Increasing velocity does not mean increasing the force
• Increasing acceleration does mean greater resultant force on an object
• For every action there is an equal and oposite reaction
• Energy
• Momentum
• All moving objects have momentum
• Momentum is the measure of how difficult it is to stop a moving object
• It is measured kgm/s
• Conservation of momentum
• Momentum before the colision is equal to the momentum after the collision.
• Impulse
• The quantity 'force x time' is known as an impulse
• The impulse measures the effect of the force
• impulse is measured in newton seconds (Ns or kgm/s)
• Circuits
• Static electricity
• Charging occurs when electrons are transferred from one material to another.
• Friction can transfer electrons
• Like charges always repel each other and unlike always attract each other
• When two electrically charged objects are brought together they exel a force on one another
• Electrodynamics
• The basic unit of eletrical charge is coulamoh (C)
• Current is easured in amps (A)
• Amps are meausred by an ammeter
• Metals are good conductors of electricity because they have free electrons that can move easily from atom to atom, so that the current flows
• Resistance
• A resistor is a componant which is made to have a certain resistance
• It helps regulate current flow
• Ohm's law: the current throught a metal wire is directly propertional to the p.d across it (providing the temperature remains constant
• The resistance of the wire is the ratio of the p.d applied across it, to the current passing through it.
• It is measured in ohnus
• Current
• Direct current (DC)
• Flows in one direction
• Bateries and cells supply a DC current
• Alternating current (AC)
• The current changes direction due to a magnet turning through a wire at the power station
• Mains electricity has a frequency of 50Hz of the current alternates 50 times a second
• Wires
• The neutral wire of a plug stays at a potential close to zero with respect to the earth
• The live wire alternates between a positive and negative potential with respect to the neutral wire
• If a fault occurs where the live wire connects to the case, the earth wire allows the large current to flow through the earth wire to the ground
• Fuses
• If the appliance develops a fault, the current may become too high. to avoid further damage we have a fuse
• A fuse  has a thin piece of wire inside it, which is the weakest link in the circuit.
• If too much current flows through the fuse the wire mealts, breaking the circuit.
• It is connected with the live wire