Physics P3

Average speed (m/s) = (u +v)/ 2 

NOTE: use this when the speed is changing uniformly 

Distance travelled = (u+v)t/ 2 

NOTE: use this when working out instantaneous speed

How fast the object is acclerating. 

the area underneath is equal to the distance travelled. 

the greater the area the faster the speed (greater acceleration)

Positive acceleration is shown by the graph sloping upwards 

Negative acceleration is shown by the graph sloping downwards

acceleartion (m/S²) = change in speed (or velocity) / time 

force = mass x acceleration 

thinking distance: tired- drugs/alcohol- travelling faster- distraction/lack of concentration 

Braking distance: poor road conditions- car is poorley mantained/ speed is increased/ heavy car 

Increase in either is unsafe as it increases the chances of an accident 

weight= mass x gravitational field strength 

power= work done/ time taken 

KE (J) = 0.5 mv2

The batteries need reacharging . Recharging uses electricity from a power station. Power station pollute the local atmosphere and cause acid rain.

momentum = mass x velocity 

force = change in momentum/ time

-Crumple zones at the front and rear absorb energy by changing shape 

-Seat belts stretch a little so some of the person's kinectic energy is converted into elastic energy 

-Air bags absorb some of the person's kinetic energy by squashing up around them 

When the weight of parachutist is greater than the air resistance- the person accelerates 

When the two are equal the person reaches a terminal speed 

When the air resistance is larger than the parachustist weight the person slows down and the air resistance decreases as they come closer to groun level 

All objects have the same acceleration point on the Earths surafce.They therefore have the same gravitational potential energy (GPE) which is 10N/kg on Earth.

loss of gravitational potential energy (GPE) = gain in kinetic energy (KE)

electrical energy--> GPE--> kentic energy 

If speed doubles KE quadruples 

If mass doubles KE doubles 

Greater distance - higher speed and greater time 

Higher speed- Greater distance and shorter time 

Greater time- Higher distance and shorter speed 

-the steeper the gradient the higher the speed

-straight lines indicates that the speed is constant 

-cruved line shows the speed is changing 

Gradient of line= acceleration 

Distance = the area under a speed-time graph

acceleartion (m/s2) = change in speed (or velocity) / time taken 

acceleration= force/mass(kg)

- Thinking distance increases linearly alongside speed so is a straight line 

-Breaking distance increases as a squarred relationship so is a curved line

power= work done/time taken 

=(force x distance)/ time taken 

=force x (distance/time)

=force x speed 

When a car stops its kentic energy changes into heat in the brakes, tyres and road.Therefore when the speed of the car doubles the kentic enrgy and the breaking distance quadruple

Hence why there are speed limits and penalties for drivers who exceed them. 

-amount of energy required to increase its kinectic energy 

-amount of energy required to do work against friction 

-speed 

-how the car is driven (excessive acceleration and decleration, constant braking and speed changed) 

-road conditions such as rough surface 

If the change in momentum happen in a short time the object will experience large acceleration or deceleration. From Newton's second law of motion this require a large force. This states F= ma

-safety features ansob energy/change shape/ reduce injure by reducing momentum therefore reduce force on the occupants 

-problems with seat belts : risk of chest injury, trapped in a fire, drivers encouraged to drive less carefully 

ABS brakes is the primary safety feature to help prevent a crash..

Wheel-seed sensors send information to a computer about the rotational speed of the wheels. The copmuter controls the pressure to the breaks via a pump, to prevent the wheels locking up. This increases the breaking force jsut before the wheels start to skid.

At first the object accelerates displacing more air particles. This creates greater air resistance so slows down the speed. Therefore ultimately the higher the spped the more air resistance. 

When weight becomes equal to air reistance the forces are balanced and there is a costant speed; terminal speed. 

-GPE varies with postion on the Earths surface 9.78N/kg at the equator and 9.83N/kg at the poles)

-GPE varies with heigh above or depth below the Earth's surface 

as the object falls friction with the air transfers the lost GPE to the surroundings.

the air particles around the object gain internal or thermal energy so increase in temperature 

mgh = 0.5 mv2

 ^m=mass 

g= acceleration due to gravity 

h= height 

v= speed