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What are the steps of the acceleration practical?
use light gate(s) to determine time and / or speed
computer calculates acceleration
repeat for different numbers of slotted masses
What is speed?
scalar quantity- magnitude (speed)
What is velocity?
vector- magnitude (speed) and direction
describes an object’s direction as well as its speed
What’s the equation for average speed?
speed= distance/ time
Adding vectors?
What’s the equation for acceleration?
acceleration= change in velocity/ time
What are the units for acceleration
m/s2
What is distance?
how far an object moves
scalar quantity- magnitude only
What is displacement?
the distance an object moves in a straight line from a starting point to a finsihing point
vector quantity- magnitude and direction
What are contact forces?
two objects are physically touching
e.g Friction, air resistance, tension and normal contact force
What are non- contact forces?
when objects are separated (not touching)
Gravitational force, electrostatic force and magnetic force
What is friction?
when two surfaces are touching and try to move against each other
tiny bumps in the surface interlock create a frictional force that opposes their motion
What’s air resistance?
when an object moves through air and collides with air molecules
creates a force that slows the object down
What’s tension?
the pulling force that a string or cable exerts when something or someone pulls on it
What’s normal contact force?
pushing on a table doesn’t make your hand move hrough it
because the normal contact force from the table pushes equally on your hand
How to use a distance time graph?
Distance-time graphs have distance on the y-axis and time on the x-axis.
On a distance-time graph, motion (movement) at a constant speed is shown by a straight line.
If the line is horizontal, then the object is stationary.
If an object is accelerating, we can measure its speed by drawing a tangent and measuring the gradient of the distance-time graph at that point.
Distance time graph
How to use a speed time graph?
Speed-time graphs have speed on the y-axis and time on the x-axis. Velocity-time graphs would simply have velocity on the y-axis instead of speed
If an object’s speed is constant, then the speed-time graph will be horizontal.
If the object is not moving (is at rest), the graph will run along the x-axis because that is where y = 0.
Acceleration determines the change in speed.
If the speed of an object increases with time, its graph will have a positive gradient.
If an object slows down, its graph will have a negative gradient.
Speed time (Velocity time) graphs
What’s mass?
a measure of the amount of matter it contains the mass of an object is constant
it is the same on Earth, on the Moon and in space
What is inertia?
a measure of how difficult it is to change an object’s motion
e.g an object with higher mass has more intertia than an object with a lower mass
it is difficult to move an object with high mass and high inertia and once it is moving, the object’s motion is hard to stop
What is the equation for weight?
Weight(N)= mass (kg) x gravitational field strength (N/kg)
What’s the centre of mass?
the point through which an object’s weight appears to act
What is the resultant force?
the sum of all the forces acting on an object
the change in an object’s motion is caused by the resultant force
if forces are unbalanced it means that a resultant force is acting on the object
What is the equation for resultant force?
Resultant force(F)= mass(m) x acceleration(a)
What’s the unit for force?
Newtons (N)
What’s the unit for mass?
Kilograms (kg)
What’s newton’s 1st law?
the velocity of an object will only change if a resultant force is acting on the object
this applies to a stationary (still) or moving object
What’s newton’s 3rd law?
whenever 2 objects interact, the forces that they exert on (apply to) each other are equal and opposite
if one object exerts (applies) a force on another object, then the other object must be exerting (applying) a force back
What does a free body diagram show?
A free body force diagram is a diagram showing the forces acting on an object shown as vectors
What is the stretching, bending and compressing?
We can stretch, bend or compress objects by applying forces to them.
For this to happen, there must be 2 or more forces acting on an object.
If only one force is acting, the object will just move in the direction of that force.
Because of this, we can normally only stretch, bend or compress stationary (still) objects
What’s elastic deformation?
an elastically deformed object will return to original shape when the force stops acting on it (spring)
What’s an inelastic deformation?
an inelastically deformed object will not return to its original shape when the force stops acting on it
What’s hookes law?
As the force on the spring increases, the spring reaches its limit of proportionality
What is the equation for hooke’s law?
force= spring constant x extension
How to set up hooke’s law practical?
Set up the apparatus as above
First, measure the original length of the spring
Next, hang different masses on the spring and measure the length of the spring in each case
Adding masses to the spring increases the downwards force as each mass has weight
The extension of the spring equals the length with masses minus the original length:
extension of the spring = length of the spring with masses − original length of the spring
Plot a graph with extension of the spring on the x axis and force on the y axis
What is work done?
When work is done, energy is transferred into an energy store
What are the types of work done on a spring?
compressing
stretching
What’s the equation for elastic potential energy?
Ee=1/2ke2
How does free dall look like on a distance time and speed time graphs?
What are the steps of air resistance?
Frictional force- opposes the motion of objects moving quickly through air
Slows a falling object- force due to air resistance increases as speed of a falling object increases
Terminal velocity- once weight force and force due to air resistance are equal, terminal velocity is the fastest the object can fall
What’s the equation for momentum?
momentum(p)= mass x velocity
What is the law of conservation of momentum?
momentum cannot be created or destroyed
What’s the unit for momentum?
kg m/s
What’s the stopping distance?
the distance it takes a car to stop
What’s the thinking distance?
the time it takes for a driver to react to a situation is their reaction time
during this tuime, the car carries on moving
the thinking distance is the distance travelled between when the driver realises they need to brake and when they apply the brakes
What’s the braking distance?
the distance the car travels between the driver applying the brakes and car stopping
What are the factors affecting thinking distance?
tiredness
distractions
drugs and alcohol
What are the factors affecting braking distance?
initial car speed
road conditions- wet or icy conditions
condition of the car- car’s brakes or tyres are in poor condition
What is the work done when braking?
pushing the brake pedal makes the brake pads press onto the wheels
causing friction causing work to be done
the work done between the brakes and the wheels converts energy from kinetic energy in the wheels to thermal energy in the brakes
temperature of brakes then increases
How does speed affect a car?
the greater the speed, the greater the braking force needed to stop the vehicle in a certain distance
meaning more work needs to be done on the brakes to stop the car
How does higher mass affect a car?
the greater the mass, the greater the braking force needed to stop the vehicle
meaning more work needs to be done on the brakes to stop the car
How does higher grip affect a car?
the stopping distance will decrease if the force (grip) between the vehicle increases
