Physics - Ls and Ps

Distance

Distance

the measure of the total path length in motion.

Displacement

measure of the total change in position of an object relative to it’s starting point.

Scalar quantity

They have magnitude size/quantity) only e.g distance. To measure they are added together.

Vector quantity

Vectors have magnitude and direction e.g displacement. To measure you use Pythagorus theory.

Speed

the rate at which something moves.

velocity

the speed of something in a given direction.

Difference between average speed and instantaneous speed

Average speed is how fast an object travelled in a given amount of time. While instantaneous speed is the speed and object was travelling at during a particular moment in time.

Acceleration

any change in speed or direction (vector quantity).

positive acceleration increases velocity while negative acceleration decreases velocity.

Stopping distance

Reaction + braking distance

Reaction distance

distance rolled while driver reacts

braking distance

Distance rolled while rolling to a stop

factors affecting reaction distance

mobile phones, drink/drug driving, tiredness of fatigue

factors affecting braking distance

tires, mass of car, road surface, speed of car

Newtons first law of motion

An object will maintain its state of motion unless acted on by an unbalanced force.

inertia

the tendency to resist change in motion

mass

the amount of matter in an object

Newtons second law of motion

the acceleration of an object depends on the mass, size and direction of an unbalanced force.

force formula

f=ma

unbalanced force:

the total force of an object once all forces have been added or subtracted

speed formula

speed = distance / time

acceleration formula

acceleration = final speed - initial speed / time

newtons third law

for every action force there is an equal opposite reaction force

N1 car safety features (act to prevent collision)

• brakes

• speed zones

• seat belts

• head rests

N2 car safety features (reduce the force of a collision → by increasing collision time, it reduces acceleration)

• crumple zones

• airbags

• collapsing steering columns.

Electricity:

the flow of charge through a circuit

Electrons

 the charged particles that can move through wires

Current

the quantity of charge (electrons) per second. Symbol: I. Unit: Amperes (A)

Voltage

the energy per charge needed to make the current flow. Symbol: V. Unit: Volts (V). It is provided by a power source

series circuit

one load resistance and only one battery

The same amount of current flows through all the components placed in it. 

parallel circuit

 two or more paths for current to flow through

The components are placed in parallel with each other due to which the circuit splits the current flow.

Ammeter

measures electric current in amperes and must be connected in series with the component.

voltmetre

measures the potential difference between two point and must be connected in parallel series 

resistance

the opposition to the flow of electric current. 

Components with high resistance will….

• will reduce how much current can flow through

• will require much higher voltage to cause current to flow

resistance equation

Resistance = Voltage/Current   → R = V/I

what is resistance used for

used to limit or control the current in a circuit. This can limit/control the power used by a component.

Variable resistors

often use a changing length of resistance wire - longer wire = higher resistance.

Variable resistors are used as:

• Volume controls for speakers

• Brightness controls for room lights

DC

• Current flows continuously in one direction through the circuit from positive to negative. One terminal is always +(positive) and the other always -(negative)

AC

• Current constantly reverses direction. Terminals switch between +(positive) and - (negative)

Earth Wire:

particular wire with low resistance and a high melting point that avoids live wire overloading and current leakage through the ground.

Casing:

• an inner metal one and an outer plastic one that cannot conduct. 

• This protects a user from touching the inner casing which could be live. It is known as double insulation

Fuses

 short length of wire in series with the circuit that will burn out and break if the current reaches a certain limit

circuit breakers

a spring-loaded switch that will heat up and pop open to break the circuit if the current reaches the limit