physics end of year
Units kg, m, m/s m/s, m/s squared, N, s, N/kg
Vectors and scalars
Vector=a quantity that has a magnitude and direction
scalar=A quantity that only has a magnitude
magnitude=the size or quantity of something
distance time graphs
If an object is accelerating it will be shown a s a curved line on the distance time graph
If it curves into a steeper gradient it is accelerating whereas if it curves into a less steep gradient it is decelerating
In distance time graphs the gradient of the line is equal to the speed of the object the greater the gradient the faster the object.
If the line is diagonal it is going at a constant speed whereas if it is horizontal it is stationary
Time always goes on the x axis in distance time graphs
equations
final velocity squared=initial velocity squared + 2 acceleration distance moved v squared=u squared + 2as
force=mass*acceleration f=ma
acceleration=(final velocity-starting velocity)/time
weight=massgravitational field strength w=mg
speed=distance/time=average speed=distance travelled/time taken
velocity time graphs
horizontal line=constant speed, horizontal line at zero=not moving, diagonal line =acceleration/deceleration, curved line =acceleration that is not constant
One can calculate the acceleration by dividing the change in velocity by the time taken for the change units=m/s/s
A velocity time graph shows the speed and direction of an object
The velocity of an object is its speed in a particular direction if two cars were heading in opposite directions they would have opposite velocities
The distance travelled can be calculated on a velocity time graph by working out the area underneath the velocity time graph
Forces can change speed direction or shape since any change in velocity is acceleration forces always result in acceleration
electrostatic and gravitational forces
gravitational=a force that attracts two objects together and pulls us towards the centre of an abject
electrostatic=when two objects are rubbed together electrons are transferred from one object to the other
Force is a vector because to describe a force you need the magnitude of it and the direction in which it is acting
If forces are balanced the object is either stationary or going at a constant speed whereas if the forces are unbalanced the object is accelerating/decelerating
Whenever an object moves against another object it feels friction. Friction makes it more difficult for things to move. Friction is a force that opposes motion
Newtons third law
e.g a cat pulls the earth up and the earth pulls the cat down
for every action it has an equal and opposite reaction
The two forces act on different objects and are of the same type e.g contact forces
If Body A exerts a force on body B Then B will exert an equal opposite force on A
a=f/m so if an object is heavier it will take a greater force to accelerate it therefore you can not push walls
terminal velocity
reaction time
braking distance=distance vehicle travels in the time after the driver has applied the brake
reaction times are affected by drugs, alcohol, tiredness and distractions all of these increase the thinking distance
thinking distance=the distance a vehicle travels in the time it takes for the driver to apply the brakes after realising they need to stop
Braking distance can be affected by poor road/weather conditions, bad brakes/tires, greater speed and the car's mass (the greater the mass the greater the braking distance)
stopping distance=thinking distance+braking distance
3) At terminal velocity the weight of the object due to gravity is balanced due to frictional forces so resultant force=0
In skydiving the parachute opens to increase air resistance and slow the terminal velocity
1) the object accelerates downwards due to gravity 2) As the object's speed increases so do drag and air resistance
All objects regardless of mass fall at the same speed without air resistance so on the moon where the gravity is too weak to have an atmosphere there is no air resistance so objects fall at the same speed
Any object falling near the earth will have an initial acceleration of 9.8m/s/s it will eventually reach terminal velocity where the resultant force is zero=steady speed
Hooke's law
The limit of proportionality refers to the point beyond which Hooke's law is no longer true when stretching a material.
The elastic limit of a material is the furthest point it can be stretched or deformed while being able to return to its previous shape.
Spring constant is a measure of the stiffness of a spring up to its limit of proportionality or elastic limit
force=spring constant*extension spring constant is measured in newtons per metre
For a given spring and other elastic objects, the extension is directly proportional to the force applied.