Forces Flashcards
Forces are a
push and pull motion
Force is measured in
Newtons
A scalar quantity is
one which only has a magnitude (size).
A vector quantity has
both magnitude and direction
examples of scalar quantities
distance, speed, mass, time, temperature
examples of vector quantities
displacement, velocity, acceleration, forces, momentum
Displacement
A single straight line from the start point to end point.
distance
the total path travelled by an object
Arrows can be used to represent vector quantities such as forces (vector diagrams):
Length of arrow corresponds to …
The direction of the arrow represents …
- the size of quantity.
- the direction at which the quantity is acting.
Contact forces
The force which is exerted between objects that are in physical contact with each other
Non-contact forces
The force exerted between two objects which are separated from each other
Examples of contact forces
friction, air resistance, normal forces, tension
examples of non-contact forces
Gravity, electrostatic, magnetism
Gravity is
the force of attraction between any 2 objects that have a mass
The higher the mass,
the stronger the force of gravity
Earth gravitational field strength
9.8N/kg
Moon gravitational field strength
1.6 N/kg
Why does the moon have a lower gravitational field strength than Earth?
It is 6 times lighter than the Earth.
Mass
The amount of matter an object has (kg).
Weight
The force exerted by an object (N).
Weight (N)=
mass (kg) x Gravity (N/kg)
Resultant force is
the overall force that acts on an object. An object can have multiple forces acting on it, but the resultant force is the single force after cancelling the forces.
forces acting in the same direction
adding forces together
forces acting in opposite directions
subtract the opposing forces
When forces are perpendicular
use Pythagoras
When forces act in angles that are not 90 degrees
vector diagrams (the line corresponds to the force itself)
work done
when energy is transferred
How to do vector diagrams
- the length of the line corresponds to the size of the force
- and work out the scale eg: 1N=1cm
- After the scale is obtained, draw a parallelogram
- This parallelogram must be drawn to scale
- Once the parallelogram is drawn connect both sides together and measure the line
- The length of the line will give the resultant force.
work done (J )equation
force (N) x distance (m)
deformation
When a force is applied to an object which results in the objects shape changing. Extension when the force applied on the object causes the shape to extend. Compression when a force is applied which makes the object smaller.
Elastic (deformation)
When the force is removed from the object, the object will return to its original shape.
Plastic/ inelastic (deformation)
when the force is removed from the object, the object will remain deformed.
Hooke’s law
Force is directly proportional to extension until the limit of proportionality.
Hooke’s law equation
F=ke
Explain the method required to work out the spring constant of a spring under investigation
1, Set up the equipment as shown above (include picture) , make sure the ruler is clamped onto the stand, so the ruler stays in a fixed position therefore increasing the accuracy of the results.
2, Record the original length of the spring by using a ruler before any masses are added.
3, Add a 0.5 kg mass onto the spring, this will cause the spring to extend.Record the extension of the spring (measure the length of the spring when it stops bouncing) (total length- original length).
4, Going up in intervals of 0.5 kg increase the mass and record the new extension value.
5, Convert all the mass values into a force by using the formula W=m x g
Force (N) Extension (m)
0kg –> 0N 0m
0.5kg –> 5 N 2m
1.0 kg–> 10N 4m
1.5 kg –> 15N 6m
2.0 kg–> 20N 8m
6, Plot the values on a graph to determine a relationship (force by extension).
7, Force/extension = spring constant. Therefore, the gradient of the graph will give the spring constant of the spring under investigation.
2 types of deformation
extension and compression
moment
The turning effect, the force that will cause an object to rotate.
Objects will turn from the central point known as
the pivot
Two directions things can turn
clockwise and anti-clockwise
The two factors that allow the turning effect to increase and decrease are:
1, Force
2, Distance from the pivot
Moment (Nm) M=
F - force (n) x D- Distance (m)
Pressure
- the force per unit area
- unit is Pa
- pressure= force/area
Principle of moments
The total anticlockwise moments is equal to the total clockwise moments.
- The object will be balanced.
Pressure in a liquid formula:
height of column (h) x density of liquid (p) x gravitational strength (g)
average speed of someone walking
1.5 metres per second
average speed of someone cyling
6m/s
average speed of sound
330 m/s
speed
A scalar quantity- only is how fast the object is going
Has no direction
velocity
a vector quantity- how fast the object is going with a direction
Has a direction
If the object travels at the same speed but changes direction velocity also changes
average speed of someone running
3m/s
speed
distance/time
sound in a more dense medium (solid)
travels faster - more vibrating matter
the steeper the gradient of a distance-time graph
the faster an object travels
acceleration
- the rate of change of velocity
- ## m/s2
acceleration equations
- v2 - u2 = 2as
- change in velocity/time
2 components to acceleration
- 1, It can either occur when something speeds up or slows down
- 2, When an object is travelling at a constant speed but changes direction, we say that it is accelerating as the direction component has been altered.
constant acceleration
getting faster at the same rate
non-uniform acceleration
the rate of speed increase is increasing as the line becomes steeper
constant velocity
the speed does not change
deceleration
negative gradient
Newton’s first law
“If an object is stationary or travelling at a constant speed it will continue to do so unless a resultant force is applied.”
If the resultant force acting on an object is zero and:
- the object is stationary, the object remains stationary
- the object is moving, the object continues to move at the same speed.
Newton’s 2nd law
“Force is directly proportional to the acceleration”
Force (N) = mass (kg) x acceleration (m/s2)
Higher force- higher acceleration
Newton’s 3rd Law
“If object A applies a force on object B, object B will exert an equal but opposite force on object A.”
- equal but opposite force
- Action- reaction pairs of forces
terminal velocity
- the maximum velocity a free-falling object reaches
- when the object has reached terminal velocity, the resultant force of the object is ZERO.
- drag and gravity are equal
terminal velocity graph
O-P : The parachutist jumps off the plane and the weight is greater than the air resistance therefore he accelerates.
P-Q: The weight remains constant however the air resistance increases subsequently causing the weight and air resistance to cancel each other out and the resultant force becomes ZERO. Reaches a constant speed known as terminal velocity
Q-R: the parachutists has activated the parachute causing air resistance to increase and therefore decelerates (becomes slower)
R-S: the parachutist again will reach a terminal velocity however this terminal velocity is a lot slower and thus will allow the person to land safely.
How to find the distance travelled from a velocity-time graph
Find the area underneath the velocity-time graph
stopping distance
thinking distance + breaking distance
Thinking distance
Reaction time, the distance travelled once the hazard has been seen and the car breaks are activated
Braking distance
The distance that the car moves after the breaks have been applied
Factors which affect stopping distance
- alcohol
- drugs
- tiredness
- vision
- distraction
- age
- health
factors which affect braking distance
- car conditions
- weather conditions
- road conditions
- speed
- break pads
- mass
momentum
It is the measure of how difficult it is to stop a moving objects
two factors which affect momentum
1, If an object is heavy like a bus it will be harder to stop than lighter objects such as a car
2, If an object is travelling really fast it will be harder to stop
momentum (kgm/s)=
mass (kg) x velocity (m/s)
conservation of momentum
the momentum before a collision= momentum after a collision
force
change in momentum/time
Why does atmospheric pressure decrease with altitude?
- the number of air molecules decreases.
What is upthrust caused by?
The pressure on the bottom of the object being greater than the pressure on the top of the object.
Explain the possible dangers caused by a vehicle having a large deceleration when it is braking
- slide
- wheels could warm up
inertia
The ability to make an object change from its motion
Explain the changing motion of the skydiver in terms of the forces acting on the skydiver. (4 marks)
- weight increases
- air resistance increases
- weight=air resistance
- terminal velocity= when the resultant force is 0
- object will continue to move at a constant speed downwards
