P10 forces and motion Flashcards
what is acceleration?
the change in velocity over a given time
what is decceleration?
when an object slows down (negative acceleration)
how do you calculate acceleration from a VELOCITY time graph?
the gradient of the graph
what is the initial acceleration of an object falling to the earth?
approximately 9.8m/s2
what is the acceleration of a falling object due to?
the force of gravity acting on the object
what do air particles cause on a falling object?
an upward force of friction to act on the object called air resistance
what is terminal velocity?
when the force of air resistance balances the force of gravity so the object stops accelerating and reaches a constant velocity
where does terminal velocity apply?
to any falling object through a fluid
what affects the terminal velocity of an object?
the shape of the object affects the amount of air resistance on the object. this affects the terminal velocity
what is Newton’s first law of motion?
if the resultant force of a stationary object is 0, it will remain stationary
if the resultant force of a moving object is 0, the object will continue to move with the same velocity
what is Newton’s second law of motion?
the acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of the object
aka - F=ma
what are the typical speeds of a car on the motorway and a normal road?
approx. 13 m/s on a typical road
approx. 30 m/s on a motorway
what is the typical acceleration of a car travelling from a road to a motorway?
2 m/s2
what is another way of describing Newton’s first law?
objects will stay still or continue to move with constant motion unless you apply a resultant force
what is inertia?
the tendency for an object to stay at rest or continue in uniform motion (due to Newton’s 1st law)
what is inertial mass?
a measure of the difficulty of changing an object’s velocity
what is Newton’s third law of motion?
whenever two objects interact, they exert equal and opposite forces on each other
what do all moving objects have?
momentum
what is the value of a stationary object’s momentum?
0
what is the conservation of momentum?
in a closed system, the total momentum before an event is equal to the total momentum after the event
what is momentum?
the product of an objects mass and velocity
what is the unit for momentum?
kg m/s
why are rapid changes in momentum dangerous?
they can cause large impact forces be exerted on an object/person, causing an injury
what are crash tests used for?
to help car manufacturers design car safety features
which two equations can be combined together to calculate the force of an object using its change in momentum?
F = ma
a = change in velocity / time
to make F = (m x v) / t (this is given in the exam)
how can the danger of rapid changes in momentum be reduced?
the overall force acting on the person can be reduced by increasing the time taken for the change in momentum to take place. this is due to the equation F = mv / t where an increase in t reduces the overall force.
what are some safety devices which slow down momentum change?
airbags
seatbelts
helmets
crash mat
cushioned surfaces
what is stopping distance?
the distance from when the driver first sees the obstruction to when the car actually stops
what are the two parts of stopping distance?
thinking distance
braking distance
what is thinking distance?
the distance travelled by the car during the driver’s reaction time
what is braking distance?
the distance the car travels from when the driver applies the brakes to when it stops
what is reaction time?
the time it takes for the driver to spot the obstruction, make a decision and then put their foot to the brake
how is the stopping distance affected due to the speed of the car?
the greater the speed, the greater the stopping distance (assuming the same force is being applied to the brakes)
what affects reaction time and stopping distance?
tiredness, drugs, distractions
what affects braking distance?
adverse road conditions (icy or wet), poorly maintained vehicles
what happens to the kinetic energy of a car if its velocity doubles?
it quadruples (x4)
what are the energy transfers involved with braking a vehicle?
the kinetic energy is transferred to thermal energy in the brakes due to the friction between the wheel and the brake
the temperature increases and the car slows down
if the speed of a car is increased, what happens to the braking force required to stop the car in a given distance?
the braking force increases
what can rapid deceleration cause in a car?
the brakes can overheat
the driver can lose control very quickly
what is an elastic object?
an object which returns to its original shape when the forces deforming it are removed
what are the conditions for elastic deformation?
an elastic material, at least two forces acting on the object
what would happen if only one force is applied to an elastic object?
the stationary object would move instead of being elastically deformed as the forces are no longer balanced
what is an inelastic material?
a material which does not return to its original shape when the forces deforming it are removed
what is inelastic deformation?
when an inelastic object has forces exerted on it and does not return to its original shape
what is Hooke’s law?
the extension of a spring is directly proportional to the force applied as long as the limit of proportionality is not exceeded
what is the limit of proportionality of a spring?
the limit for Hooke’s law applied to the extension of a stretched spring
it is when the spring no longer returns to its original length
what is the spring constant of a spring?
the force per unit extension needed to extend the spring.
it is a measure of the stiffness of the spring
