SP2 Motion and Forces Flashcards
(21 cards)
Define a resultant force
The overall force acting on an object
Newton’s 1st Law
If the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it’ll just carry on moving at the same velocity
What is a centripetal force?
A force that keeps something moving in a circle
Why does circular motion keep changing velocity?
If an object is travelling in a circle, it is constantly changing direction, so it is constantly changing velocity: this means its accelerating
Define mass
Mass is just the amount of “stuff” (matter) an object is made up of
Define weight
Weight is the force acting on an object due to gravity
Formula for weight
Weight (N) = mass (kg) x g
How is the weight of an object affected by gravity?
Gravitational field strength varies with location; it’s stronger the closer you are to the mass causing the field
Newton’ 2nd Law
F = m x a
Define inertial mass
An object’s inertial mass measures how difficult it is to change the velocity of an object.
Rearranging Newton’s 2nd Law gives m = F / a, so inertial mass is just the ratio of force over acceleration
Newton’s 3rd Law
When two objects interact, the forces they exert on each other are equal and opposite
Formula for momentum
momentum (kg m/s) = mass (kg) x velocity (m/s)
Formula for change in momentum
force = change in momentum / time
Define thinking distance
The distance the car travels in the driver’s reaction time
Factors affecting thinking distance
1) Tiredness, alcohol, drugs and distractions
2) Your speed
Define braking distance
The distance taken to stop once the brakes have been applied
Factors affecting braking distance
1) Your speed
2) Mass of car
3) Condition of the brakes
4) Friction between road and tyres
How is work done on a car?
Brakes do work on the car’s wheels - this transfers energy from the car’s kinetic energy store to the thermal energy store of the brakes
Define ‘large decelerations’
A greater braking force produces a greater deceleration
Dangers of ‘large decelerations’
Serious injuries as a large deceleration requires a large force - this force can be lowered by slowing over a longer period
Safety features in cars
1) Seat belts stretch slightly
2) Air bags slow you down gradually
3) Crumple zones increase time taken to stop
