1 Forces and Motion Flashcards
Equation for speed
Distance/time
Practical: investigate the motion of everyday objects such as toy cars or tennis balls
- Connect a trolley to a ticker tape timer (fitted with a ticker tape) and position on a slope
- Release the trolley.
- Take a 5-dot section
- Work out distance of this section
- Divide by 50 (ticker tape timer is set to 50 times per second)
Equation for acceleration
Change in velocity (final - initial)/time
Distance - Time Graphs
Gradient = velocity
Velocity - Time Graphs
Gradient = acceleration
Area under graph = distance or displacement
Equation for final speed
v2 = u2 + (2 × a × s)
Vector Quantities
Has magnitude + direction
Scalar Quantities
Has magnitude
Pulling Force
Tensile Force
Pushing Force
Compressive Force
What is the length of the arrow proportional to?
The size of the force
Forces acting on an object
- Weight
- Friction
- Reaction force (opposes weight)
Friction
Force that opposes motion
Resultant Force
front force - back force
* If positive = acceleration
* If negative = deceleration
How can frictional forces occur?
- When one surface rubs against another surface
- When a body moves through a fluid
Investigating Friction
- Put masses in shoe
- Hook shoe to force meter
- Pull force meter
Equation for force
Mass x Acceleration
Equation for Weight
Mass x Gravitational Field Strength
Equation for stopping distance
Thinking Distance + Braking Distance
What is friction in relation to weight?
Directly proportional
Weight
- The force in which gravity pulls it down
Factors that increase thinking distance
- High initial velocity
- Alcohol + drugs
- Tiredness
- Distraction inside car
Factors that increase braking distance
- Poorly maintained brakes
- High initial velocity
- Road condition/surface
- Worn tyres
Newtons 2nd Law
When an object experiences a resultant force it will accelerate. The magnitude of the acceleration is proportional to the force
How an object reaches terminal velocity
- There is an unbalanced force
- W>D so acceleration
- W=D so no acceleration so constant terminal velocity
After parachute opens - W<D so deceleration
- W=D so constant terminal velocity
Equation for momentum
Mass x velocity
Conservation of momentum
Provided there are no external forces on a system, total momentum is conserved.
Momentum before = Momentum after
Momentum for safety features
If time taken can be increased for a change in momentum, the force on the body can be decreased. This is done by airbags with inflate quickly and deflate slowly as the person hits them to slow them down
Equation for force in terms of momentum
Change in momentum/time
Hooke’s Law
The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality
The limit of proportionality in Hooke’s Law
if more force is added, the object may extend but will not return to its original shape when the force is removed (it will be inelastically deformed)
Elastic behaviour
the ability of a material to recover its original shape
after the forces causing deformation have been removed
Practical: investigate how extension varies with applied force for helical springs, metal wires and rubber bands
Newton’s 3rd Law
To every force there is an equal and opposite reaction
Equation for moment
Moment = force x perpendicular distance from the pivot
Where does the weight of a body act from?
Its centre of gravity
Principle of moments
Clockwise moment = anticlockwise moment
What do forces cause?
A change in motion
What factors affect drag?
- Velocity
- Surface Area
Axis on Hooke’s Law graph
x - axis: Force
y - axis: Extension
Does a wire obey Hooke’s law?
Initial yes, but then goes up on graph
Does an rubber band obey Hooke’s law?
How are the independent variable and the dependant variable placed on the axis of a graph
- Independent variable: x - axis
- Dependant variable: y - axis
What type of graph does a continuous variable need?
Scatter graph
How to work out the gradient
Up/accross
How to find the centre of gravity of an irregular shape
- Take a mounted needle with a plumb line attached to it
- Place the mounted needle at the top and draw where the plumb line goes
- Rotate and repeat
- The point of intersection is the centre of gravity
What is a moment?
The turning effect of a force
When does the principle of moments apply?
When an object is balanced or in equilibrium
