Forces And Their Effects Flashcards
What are scalar quantities?
- They have magnitude only
What are vector quantities?
- they have magnitude and an associated direction
List the scalar quantities:
- speed
- time
- distance
- temperature
- mass
- length
- energy
List the vector quantities:
- velocity
- force
- displacement
- acceleration
- momentum
- weight
What is the formula for velocity?
- velocity= displacement (distance in a given direction) / time taken
- s = v x t
What does the gradient equal in a distance-time graph?
- speed
What do the flat sections of a distance time graph represent?
- stationary
- stopped
What do the curves represent in a distance time graph?
- acceleration
- deceleration
What is acceleration?
- how quickly the velocity is changing
- this change in velocity can be a change in speed or a change in direction (or both)
What is the formulae for acceleration?
- acceleration = change in velocity / time taken
- a = (v - u) / t
What does the gradient represent in a velocity time graph?
- acceleration
What do the flat section represent in a velocity time graph?
- steady speed
What is a resultant force?
- the overall force in a point or object
- whenever two objects interact, the forces they exert in each other are equal and opposite
What will happen to a stationary object if the resultant force was
1) zero
2) not zero
1) the object will remain stationary
2) the object will accelerate in the direction of the resultant force
What will happen to a moving object if the resultant force is
1) zero
2) not zero
1) the object will continue to move at the same speed and in the same direction
2) the object will accelerate in the direction of the resultant force
What is the equation to find the resultant force?
- F = ma
What is momentum (p) ?
A property of moving objects
When is there more momentum?
- the greater the mass of an object and the greater its velocity, the more momentum it has
Why is the equation for momentum?
- p = m x v
- momentum (kg m/s) = mass (kg) x velocity (m/s)
What is the Conservation of Momentum?
In a closed system, the total momentum before an event is the same as after the event
What causes a change in momentum?
- when a force acts on an object
What is the equation between force c change in momentum and time?
- force acting (n) = change in momentum (kg m/s) / time take for change to happen (S)
- 🔼p = F x t
Why do safety features in a car increase the collision time?
- this decreases the rate of change of momentum and so reduces the forces on the passengers
What do seat belts do?
- seat belts stretch slightly, increasing the time taken for the wearer to stop
- this decreases the rate of change of momentum and so reduces the forces acting in the chest
What to air bags do?
- slow us down more gradually
- decreases the rate of change of momentum
- reduces the forces acting on the chest
Why would an object with no force propelling it along always slow down and stop?
- because of friction
What direction does friction act?
- the opposite direction of movement
How can you travel at a steady speed?
- the driving force needs to balance the frictional forces
What happens to frictional forces/drag with speed increases?
- they also increase
Why do objects falling through fluids reach a terminal velocity?
- when falling objects first set off, the force of gravity is much more than the frictional force slowing them down
- so they accelerate.
- as the speed increases the friction builds up
- this gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force
- then it will have reached terminal velocity and fall at a steady speed
What is a total stopping distance?
- the distance covered in the time between the driver first spotting a hazard and the vehicle coming to a complete stop
- the sum of the thinking distance and the braking distance
What is thinking distance?
- the distance the vehicle travels during the driver’s reaction time
What factors affect thinking distance?
- how fast you’re going: faster you go, further you’ll go
- tiredness, drugs, alcohol, carelessness.
- bad visibility and distractions.
What is braking distance?
- the distance the car tracked under the braking force
What factors affect braking distance?
- how fast you’re going: faster you’re going, further it takes to stop
- how good brakes are
- how good tyres are: need a minimum tread depth of 1.6mm
- how good grip is: depending on road surface, weather conditions and tyres
What is weight?
- weight is caused by the pull of the gravitational force
What is the Formula for weight?
- W = m x g
- weight = mass x gravitational field strength
What happens when a force moved an object through a distance?
- energy is transferred
- work is done
What is the formula for work done?
- work done = force x distance
- W = F x d
What is gravitational potential energy (measured in joules)?
- it is the energy that an object has by virtue of its vertical position in a gravitational field
- when an object is raised vertically, work is done against the force of gravity and the object gains GPE
- gravitational field strength is approx 10N/kg on earth
What the formula for gravitational potential energy?
- GPE = mass x g x h
- Ep = m x g x h
What is kinetic energy?
- the energy of movement
What is the formula for kinetic energy?
- kinetic energy = 1/2 x mass x speed^2
- Ek = 1/2 x m x v^2
What is work done?
- The transfer of kinetic energy
What is the equation for kinetic energy transferred?
- kinetic energy transferred = work done by brakes
- 1/2mv^2 = F x d
What is work done to an elastic object stored as?
- elastic potential energy
- when a force is applied to an object you may stretch it and it may change in shape.
- it is stored as EPE
What happens when an elastic object is extended?
- the extension, e, of a stretched spring is directly proportional to the lord or force applied , F.
- F = k x e
- k is the spring constant. Measured in N/m
What is the limit of proportionality ?
- there is a maximum force that the elastic object can take and still experience proportionally.
- this is known as the limit of proportionality.
What is power?
- power is the rate of doing work
- measured in watts
- one watt = 1 joule of energy transferred lee second
What is the formula for power?
- Power = work done (or energy transferred) / time taken
- P = W / t
What is the time period of a pendulum?
- the time taken for the pendulum to swing from one side to the other and back again
Why are pendulums perfect for keeping time in clocks?
- the time period for each swing of a pendulum is always the same
What formula can calculate time worked?
- Time period = 1 / frequency
- T = 1 / f
What does the time period depend on?
- the length
- the longer the pendulum, the greater the time period
What is circular motion?
- if an object is travelling in a circle it is constantly changing direction
- this means velocity is constantly changing (but not speed)
- so object is accelerating, towards the centre of the circle.
What is centripetal force?
- the force that keeps something moving in a circle
- the resultant force acting on the object causing acceleration
When does the centripetal force needed to make an object perform circular motion increase?
- as the mass of the object increases
- as the speed of the object increases
- as the radius of the circle decreases
What is the centre of mass?
- the centre of mass of an object is the point at which the mass of the object seems to be concentrated
Where will an object come to rest if free suspended?
- at its centre of mass directly below the point of suspension
Where is the centre of mass of a symmetrical object?
- along the axis of symmetry
What is the equation for the size of a moment?
- moment = force x perpendicular distance from the line of action of the force to the pivot
- M(Nm) = F(N) x d(m)
What is the moment?
- the turning effect of a force
Why would using a longer spanner exert a larger moment?
- the distance from the pivot is greater
- less force is needed to get the same moment
How do you get the maximum moment?
- push at right angles (perpendicular) to the spanner
What happens when an object is not turning?
- the total clockwise moment must be at equilibrium with the total anticlockwise moment at any pivot
What are simple levers known as?
- force multipliers
- they reduce the amount of force that’s needed to get the same moment by increasing the distance
Give three examples of simple levers
- long sticks or bars
- wheelbarrows
- scissors
What makes an object stable?
- a wide base
- a low centre of mass
What makes an object tip over?
- if the line of action of the weight of the object lies outside the base of the object, it will cause a resultant movement
- therefore it tips over
Can liquids be compressed?
- no, they are virtually incompressible
What happens when a force is applied to one point in the liquid?
- it will be transmitted to the other point in the liquid
- pressure in a liquid is transmitted equally in all directions
Give the equation for pressure
- Pressure = Force x cross-sectional area
- F(N) = P(Pa) x A (m^2)
What are hydraulic systems used as?
- force multipliers
What are the two pistons in a hydraulic system?
- master piston: smaller cross-sectional area
- slave piston: larger cross sectional area
Describe how a simple hydraulic system works
- at the master piston, the pressure is exerted on the liquid using a small force over a small area
- this pressure is transmitted to the slave piston
- the slave piston has a larger area, so due to F = P x a, there will be a larger force
What are hydraulic systems used for?
- car braking systems
- hydraulic car jacks
- manufacturing and deployment of landing gear on some aircraft
