# Physics- key stuff

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## Distance- time graphs

• The steeper the gradient, the faster the speed.
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• Straight line= constant speed.
• --------------------------------------------------
• Flat horizontal= standing still
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• Curved = acceleration
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## Velocity graphs

• Straight line= acceleration

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• Flat horrizontal= constant speed

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• Distance travelled = area under graph
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## Force

• Units for force: N
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## Momentum

mom= m x v

• Momentum is a vector.
• -------------------------------------------------------------
• Unit for momentum= kgm/s

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Explosions:

Mom before = mom after

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## Stopping Distance

Reaction time: how long it takes to see someting, process it, and react.

Thinking distance:the distance moved (in car) when you are processing something (dog in road).

Breaking distance: the distance travelled once you have hit the breaks.

stopping distance= thinking + breaking

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## Factors affecting stopping distance stuff

Factors affecting reaction time:

• drugs
• tiredness
• age
• drunkness

Factors affecting breaking distance:

• condition of car
• massof car
• speed of car
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## Hooke's Law- Extention

Extention= new length - orginal length

• force= mass x gravity
• gravity= 10
• curve on top of line graph is the elastic limit!

spring constant= Force / extention

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## Terminal velocity

Terminal velocity:

• 0 resulutant force
• 0 acceleration
• costant speed

Faster= more air resistance

• Eventually, all energy is used up to overcome air resistance.
• =forces are balanced when object is falling.
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## Energy

Work done= force x distance moved

Units for energy: joules

Power = work done / time taken

1 watt = 1J / 1s

EP= m x g x h   Gravitational potential

EK= 1/2 mv    Kinetic

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## Moments

Moment- turning effect of a force (pivot)

moment of force= force x perpendicular distance from pivot

• Moments have a direction
• .
• Centre of mass:   point where an object's mass is

.thought to act through

• wide base = more stable
• lower centre of mass = more stable
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## Circular motion + pressure

Circular motion:

• Velocity has a direction, as is changeing. If velocity changes, there must be an accelaration. Therefore, an object going at the same speed can be accelerating (in a circle)
• Centripetial force: force acting towards centre of mass.
• .

Pressure:

pressure= force / area

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## Lenses

Convex/ converging: forms a real image.

Concave/ diverging: forms a virtual image.

Lense Formula:  1   +     1  =      1                                u          v         f

Magnification:  image height                                        object height

Power of Lense:       1                                                 focal length

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## The eye

Short sight: light focuses too quickly. Only see close objects                             clearly.

correction: diverging lense.

Long sight: light focuses behind retina. Only distant objects                             clearly.

correction: converging lense.

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## Electric current

If an object looses electons it becomes positive

If an object gains electrons it becomes negative.

Ion: a charged atom

Electric current: a flow of charge. Measured by an ammeter. AMPS

Battery: two or more cells connected together.

current=  charge flow                                                                 time taken

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## Potential Difference

Potential Difference:                   Voltage = potential difference

A mearure of energy transferreent across a component

Meassured by volt meter. VOLTS.

potential difference=  energy transferred                                                       charge

Resistance: ions resit the passage of electrons

Measured in : ohms

resistance= potential difference  Larger resistance= smallercurrent                    current

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