Scalar quantities have
Magnitude only (size)
A vector quantity has
Magnitude and direction
Represent vector quantities using
Arrows
Length shows the magnitude
Points in the direction that the vector quantity is acting
Forces are …….. quantities
Vector
A force occurs when
Two or more objects interact
Forces are either
Contact so objects are touching
Non contact so objects are not touching
Example of contact forces
Friction Air resistance/drag Tension Normal contact force Upthrust
Examples of non contact forces
Gravitational force
Electrostatic force
Magnetic force
Gravity is
A force of attraction between all masses
The force of gravity close to earth is due to the
Gravitational field around the planet
The mass of an object is related to the
Amount of matter it contains and is constant
Weight is
The force acting on an object due to gravity
The weight of an object depend on
The gravitational field strength where the object is and is directly proportional to its mass
Formula for weight
Weight =
mass x gravitational field strength
Résultant force
When more than one force acts on an object These forces can be seen as a single force that has the same effect as all the forces acting togerh r
A free body diagram can be used to show
Different forces acting on an object
Scale vector diagrams are used to illustrate the overall effect when more than one force acts on an object
The forces are added together to find a single resultant force, including both magnitude and direction
The vectors are added head to tail and a resultant force arrow is drawn
Scale vector diagrams can also be used when a force is acting in a diagonal direction
Expressing the diagonal force as two forces at right angles to each other can help work out what effect the force will have
The force F(r) can be broken into F(1) and F(2)
F(1) is the same length of F(r) in the horizontal direction
F(2) is th same length of F(r) in the horizontal direction
When a force causes an object to move
Work is done on the object
This is because it requires energy to move the object
One joule of work is done when
One Newton is moved one metre
Work done formula
Work done= force x distance
When work is done
Energy transfers take place within the system
To change the shape of an object
More than one force much be applied
Elastically deformed =
If an object returns to its original shape after forces are applied
Inelastically deformed
Object does not return to its original shape after force is applied
The extension of an elastic object is directly proportional to
The applied force
Once the limit of proportionality has been exceeded:
Doubling the force will no longer exactly double the extension
The relationship become non linear
A force-extension graph will stop being a straight line
Equation which applies to the linear section of a force extension graph
and to the compression of an elastic object
Force = spring constant x extension
Spring constant indicates
How easy it is to stretch or compress a spring
Higher it is the stiffer the spring is
A force that stretches or compresses a spring contains
Elastic potential energy
The amount of energy done and the work stored are
Equal providing the spring does not go past the limit of proportionality
Required practical
Pg11
When a force causes an object to rotate about a pivot
The turning effect is called a moment of a force
Moment of a force equation
Force x distance
If an object is balance, the total clockwise moment about the pivot equals
The total anti-clockwise moment about that pivot
F1xd1=f2xd2
What increases when the applied force moves further than the transmitted force
The force
What increases when the applied force is bigger than the transmitted force
The distance
A fluid
Liquid or gas
Particles in a fluid
Collide with the surface of objects or container
Pressure equation
Force normal to surface /
Area of that surface
If the pressure acts on a bigger area
It will produce a larger force
The atmosphere is
A relatively thin layer of air around the earth
The greater the altitude
The less dense the atmosphere and the lower the atmospheric pressure
At high altitude
There is less air above a surface than at lower altitudes, so there is a smaller weight of air acting on the surface and the equation
P=f/a will result in a lower pressure
Résultant force
When more than one force acts on an object These forces can be seen as a single force that has the same effect as all the forces acting togerh r
A free body diagram can be used to show
Different forces acting on an object
Scale vector diagrams are used to illustrate the overall effect when more than one force acts on an object
The forces are added together to find a single resultant force, including both magnitude and direction
The vectors are added head to tail and a resultant force arrow is drawn
Scale vector diagrams can also be used when a force is acting in a diagonal direction
Expressing the diagonal force as two forces at right angles to each other can help work out what effect the force will have
The force F(r) can be broken into F(1) and F(2)
F(1) is the same length of F(r) in the horizontal direction
F(2) is th same length of F(r) in the horizontal direction
When a force causes an object to move
Work is done on the object
This is because it requires energy to move the object
One joule of work is done when
One Newton is moved one metre
Work done formula
Work done= force x distance
When work is done
Energy transfers take place within the system
To change the shape of an object
More than one force much be applied
Elastically deformed =
If an object returns to its original shape after forces are applied
Inelastically deformed
Object does not return to its original shape after force is applied
The extension of an elastic object is directly proportional to
The applied force
Once the limit of proportionality has been exceeded:
Doubling the force will no longer exactly double the extension
The relationship become non linear
A force-extension graph will stop being a straight line
Equation which applies to the linear section of a force extension graph
and to the compression of an elastic object
Force = spring constant x extension
Spring constant indicates
How easy it is to stretch or compress a spring
Higher it is the stiffer the spring is
A force that stretches or compresses a spring contains
Elastic potential energy
The amount of energy done and the work stored are
Equal providing the spring does not go past the limit of proportionality
Pressure at a particular point in a column of liquid depends on
The height of the column above the point
The density of the liquid
The higher the column and the more dense the liquid
The greater the weight above the point
The greater the force on the surface at that point
The greater the pressure
Pressure equation
Height of the column X density of the liquid X gravitational field strength
When an object is submerged in a liquid
There is a greater height of liquid above the bottom surface than above the top surface
The bottom surface of experiences a greater pressure than the top surface and this creates a resultant force upwards
Upthrust is
The upward force exerted by fluid on the submerged object
Object floats when
Its weight is equal to the upthrust
And object sinks when
Its weight is greater than the upthrust
Weather and object will float or sink depends on
The density
If an object is less dense than the liquid
Displaces volume of liquid greater than its own weight so it will rise to the surface
Will float with some of the objects remaining below surface
Displaces liquid of equal weight to the object
If an object has a low-density
More of the object will remain above the surface
Size of upthrust it’s always equal to
The weight of liquid displaced
An object denser then the surrounding liquid cannot
Displace enough liquid to equal its own weight so it sinks
Distance
Scalar quantity
How far and object moves
Does not take into account the direction and object is travelling in or even if it ends up back where it started
Displacement
It has a magnitude, which describes how far the object has travelled from the original in a straight line
It has direction which is the direction of the straight line
Vector quantity
Speed measure
How fast something is going
Scalar quantity
M/s
Distance =
Speed x time
Velocity is
Vector
Speed of am object In a given direction
When travelling in a straight line and object with constant speed also has
Constant velocity
If an object is not travelling in a straight line
The speed can still be constant but the velocity will change because the direction has changed
object moving in a circle
Constantly changing direction so constantly changing velocity it is accelerating even if it is at a constant speed
Eg orbiting planets
Newton’s first law
An object will remain in the same state of motion unless acted on by an external force
When the resultant force is zero
Remains stationary if already
If moving stays at a constant velocity
This is called inertia
Velocity only changes if
Theee is a resultant force
Distance time graph represents
The motion of an object travelling in a straight line
Gradient of a distance time graph shows
Speed
Distance time graph is a curve if
It is accelerating
Tangent to figure it out
Acceleration is
How quickly something speeds up slows down or changes direction
Acceleration equation
Acceleration =
Change in velocity /
Time taken
Acceleration is negative when
An object slows down
Uniform acceleration equation
Final velocity^2 —initial velocity ^2=
2 x acceleration X distance
Gradient of a velocity time graph
Acceleration
Area under at velocity time graph
distance
Newtons second law
The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to to the mass of the object
If the resultant force is doubled the acceleration will be doubled
If the mass is doubled the acceleration will be halved
Newtons law equation second
Force = mass X acceleration
Mass is a measure of
Inertia
It describes how difficult it is to change the velocity of an object this inertial mass is given by the ratio of force over acceleration the larger the mass the bigger the force needed to change the velocity
Required practical
Pg 17
When an object falls through a fluid
At first the object accelerates due to the force of gravity
As it speeds up the resistive forces increase
The resultant force reaches zero when the resistive forces balance the force of gravity. At this point the object will fall at the steady speed called terminal velocity
Acceleration near the earths surface is
10m/s^2
Due to gravity
Newton’s third law is
For every action there is an equal and opposite reaction
When one object exerts a force on another
The other object exerts a force back
Same type and equal in size but opposite in direction
Momentum equation
Mass x Velocity
A change in momentum occurs when
Unbalanced force acts on an object that is moving or able to move
Change in momentum equation
Force =Change of momentum/changing time
Safety devices reduce
The forced by increasing the time over which change in the momentum takes place
In a closed system the total momentum before and event is equal to
Total momentum After an event
Most often referred to during collisions
The stopping distance of a vehicle depends on
The thinking distance and the braking distance
For a given braking distance
The greater the speed of the vehicle the longer the stopping distance
Thinking distance is directly proportional to
Speed
If you double the speed the braking distance increases
By a Factor of four
Reaction times for humans
0.2-0.9 seconds
Reaction time can be affected by
Tiredness, drugs, alcohol, distractions
Braking distance can be affected bye
Condition of road, the vehicle, the weather
Wet or icy
Worn brakes and tyres and over inflated or underinflated tires
The greater the braking force
The greater the deceleration
To stop the vehicle
Breaks need to apply force to the wheels
Temperature of brakes increases by
Work done that by frictional force transfering kinetic energy to heat energy
If the braking force is to large
The brakes might overheat all the tires May lose traction on the road resulting in skidding
More likely if tires and brakes are in poor conditions
Find the size of breaking force equation
Work done (kinetic energy) = force X distance (breaking distance)
For a given braking distance
Doubling the mass doubles the force required
Doubling the speed quadruples the force required