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What is speed?
how fast something is going
How do you work out the speed?
speed= distance ÷ time
What is velocity
speed with direction
What do distance-time graphs show?
how something is travelling over a period of time
What is the gradient of a distance-time graph equal to?
speed- how fast the object is travelling
What does the downwards gradient on a distance-time graph show?
it means its going back towards its starting location
What do the flat sections on a distance-time graph mean?
it's stationary
What do straight up hill or down hill sections mean?
it's travelling at a steady speed
The steeper the distance-time graph...
the faster it's going
What do curves represent in a distance time graph?
acceleration (steepening curve) or deceleration (leveling off curve)
How to work out the speed on a distance-time graph?
the change in y ÷ the change in x
What is acceleration?
how quickly the velocity is changing
What can the change in velocity be?
change is speed or a change in direction
What is the formula for acceleration?
acceleration= change in velocity ÷ time taken
What does the gradient equal on velocity-time graph?
acceleration
What does the flat sections on a velocity-time graph represent?
steady sped
The steeper the velocity-time graph...
the greater the acceleration or deceleration
What do the uphill sections mean on a velocity-time graph (/)?
acceleration
What do the downhill sections mean on a velocity-time graph ()?
deceleration
What does the area under any section of the velocity-time graph (or all of it) mean?
distance travelled in that time interval
What does a curve mean on a velocity-time graph?
changing acceleration
What is the unit of acceleration?
m/s²
What are gravity's two important effects?
on the surface of a planet, it makes all things accelerate towards the ground
it gives everything a weight
What is mass?
amount of stuff in an object
What is the unit of mass?
kg
What is weight?
the pull of the gravitational force towards the centre of the Earth
What is the unit of weight?
newtons
What is the formula relating mass, weight and gravity?
weight= mass x gravitational field strength
What is the resultant force?
the overall force on a point/object
How do you calculate the resultant force?
one force + another force
If resultant force is 0 it means that...
the object won't move
If there is no resultant for on a moving object it means that...
it will move at a constant velocity
If the resultant force on an object is not 0 it means that...
the object will accelerate in the direction of the force
What does a non-zero resultant force produce?
acceleration
What is the formula for resultants force?
resultant force (N)= mass (kg) x acceleration (m/s²)
What are the different forms of acceleration?
speeding up, steady speed, starting
When two objects interact, the forces they exert on each other are...
equal and opposite to each other
Friction is always there to...
slow things down
Friction regarding direction of movement...
acts in opposite direction
How can we reduce air resistance?
bykeeping shape streamlined
Drag increases as...
the speed increases
What is the terminal velocity?
maximum speed an object reaches and will then remain at a steady speed
What factors does terminal velocity depend on?
shape and area
What factors affect your total stopping distance?
thinking distance and braking distance
What is the reaction time?
the time between the driver spotting the hazard and taking action
factors affecting thinking distance
how fast you're going
how dopey you are due to alcohol, fatigue, drugs or carelessness
bad visibility due to weather, or bright oncoming lights
distractions
What are the factors affecting your braking distance?
how fast you're going
how good brakes are
how good tires are, how good grip is on road- ice/rain
What happens when a force moves an object?
energy is transferred and work is done
What is the formula or work done?
work done= force x distance
What is gravitational potential energy?
it is energy that an object has depending on its height, the work done against the force of gravity
What is the formula for gravitational potential energy?
gravitational potential energy= mass x g x height
What is kinetic energy?
anything that is moving has kinetic energy
(the more it weighs, the faster its going, the bigger the kinetic energy will be)
What is the formula for kinetic energy?
1/2 x mass x speed²
For a car to slow down kinetic energy must be...
converted into other types of energy
For a car to stop, the kinetic energy must be...
converted into heat energy as friction between the wheels and the brake pads, causing the temperature in the brakes to increase
How do you calculate kinetic energy gained when falling?
kinetic energy gained= potential energy lost
What can potential energy be transferred into?
heat and sound energy
Elastic objects are...
objects that will return to its original shape when bent or shaped
What is the energy stored in an elastic object when bent?
elastic potential energy
The extension of an elastic object is...
directly proportional to the force applied
What is the equation that links together extension, spring constant and force?
force (N)= spring constant (n/m) x extension (m)
What happens when you pull an elastic object beyond its limit of proportionality?
it will not extend as much with the same force due to the limit of proportionality
What is power?
the rate of energy transferred
What are powerful machines?
a machine that transfers a lot of force in a short space of time
What is the unit of power?
watts or joules per second
What is the formula for power?
power= work done (or energy transferred) ÷ time taken
What is the definition of momentum?
a property of moving objects- size and direction (it is a vector quantity)
What is the formula of momentum?
momentum (kg m/s)= mass (kg) x velocity (m/s)
What is conservation of momentum?
in a closed system of momentum, total momentum before an event is the same as after
In what way do forces cause changes in momentum?
forces act on an object cause a change in momentum
larger force means a faster change of momentum
if someones momentum changes very quickly (e.g. in a car crash) the forces on the body will be very large, and more likely cause an injury
Why are cars designed with safety features?
to slow people down over a long time when they have a car crash
the longer it takes for a change in momentum, the smaller the force
What do breaks do?
reduce the kinetic energy of the car by transferring it into heat energy
What is the difference between standard brakes and regenerative brakes?
standard brakes= kinetic energy into heat energy
regenerative brakes put motor running backwards- electricity generated and stored
How are cars designed to convert kinetic energy safely in a crash?
crumple zones at front and back of car
seat belts
air bags
side impact bars
What do crumple zones do?
crumple upon impact
cars kinetic energy is converted into other forms of energy by the car body as it changes shape
the increase the impact time
decrease the force produced by the change in momentum
What do seat belts do?
stretch slightly
increase the time taken for the wearer to stop
this reduces the forces acting in the chest
some kinetic energy of the wearer is absorbed by the seat belt stretching
What do airbags do?
slow you down more gradually
prevent you from hitting the hard surfaces inside the car
What do side impact bars do?
strong metal tubes fitted into car door panels
