Topic 5 – Forces Fundamentals Flashcards
give 6 examples of scalar quantities
mass, temperature, speed, energy, distance, time
give 6 examples of vector quanitities
displacement, weight, force, velocity, acceleration, momentum
give 4 examples of contact forces
tension, friction, air resistance, normal contact force
give 3 examples of non contact forces
gravitational force, electrostatic force , magnetic force
weight of an object is ___ to the mass of the object
directly proportional so if we double the weight we double the mass
what is the centre of mass
when the weight of an object can be considered to be acting at a single point
what is a resultant force
a single force that has the same effect as all of the original forces acting together
how do we work out resultant force
subtract smaller force from larger force and state direction
whats the opposite force to weight in the air?
lift
whats the forward force for aeroplanes provided by the engines called
thrust
what is work
when a force is used to move an object & energy is transferred
when calculating work done, distance must be ________ of the force
in the line of action
whats the equation for work done
force x distance
in an elastic material, the stretching forces are equal in ______ but opposite in ____
magnitude, direction
what do you have to do to change an objects length or shape
apply more than one force
why cant you change the length or shape of an object by applying only one force?
the forces would no longer be balanced so the object would move instead of changing shape/length
What’s a good example of inelastic materials
certain polymers
whats inelastic deformation
when inelastic materials do not return to their original shape when stretched
when we stretch/ compress, we’re using a force to do work so elastic potential energy is stored so work done = elastic potential energy. When is this NOT true?
if the object is NOT inelastically deformed
how to set up required practical 6: stretching a spring
setting up a clamp stand w/ 2 bosses and two clamps,, place a heavy weight on clamp stand to prevent it falling over,,,attach metre ruler and a spring,,, top of the spring needs to be at 0 on the metre ruler ,,, metre rule must b verticle for accurate readings ,,, bottom of spring has wooden splint attached as a pointer
how to take readings for required practical 6: stretching a spring
read the position of the pointer on the metre ruler, this is the unstretched length of the string (the length with NO force attached),,, then hang a 1N weight on the spring & read the new position of the pointer,,,, continue adding 1N weights to the spring and reading the position of the pointer then work out the extension produced by adding each weight by subtracting the length of the unstretched spring from each reading then plot the extension against the weight
how would you find out the weight of a mystery object
measure the extension of the spring when the object is hanging from it ,,, read the weight of the object from the graph
what happens when a spring is overstretched
is exceeded the limit of proportionality
whats the unit for moments?
Nm (newton metre)
what do we know about moments if the seesaw is balanced
the clockwise moment = the anticlockwise moment
how do blocks topple
blocks on a flat surface ,,, the weight of the block act directly down from the centre of mass,,, there comes a point where the line of action lies outside of the base of the object so now theres a resultant moment acting on the block
what is a moment
the turning effect of a force
levers are what?
force multipliers
what does the turning effect depend on
the distance between the edge of the gear and the centre
in water, the bottom of the object experiences a _____ pressure than the top
larger
when does an object sink?
if the upthrust is less than the object’s weight
size of the upthrust acting on the object is equal to what?
the weight of water displaced
what does speed depend on
age and fitness,,, the terrain,, distance travelled
what are some average speeds
walking= 1.5,,,,
running = 3,,,,
cycling= 6 ,,,
car on road = 13 ,,,,,
fast train in UK = 50 ,,,,
cruising aeroplane = 250 ,,,
what do you have to remember to do when calculating velocity?
stating the direction
what happens if an object moves at constant speed in a circle
if an object moves at a constant speed in a circle then its velocity is constantly changing even though its speed is constant
how to work out speed froma distance time graph
the gradient (distance/time)
the gradient of a velocity time graph tells us what?
the acceleration
what does a negative gradient tell us in a velocity time graph
the object was decelerating
how to find distance travelled in a specific direction using a distance-time graph
the total area under the graph
how to find the distance travelled ina. NON CONSTANT velocity-time graph
counting the number of squares (estimate how many there are) then multiply by area of square
when an object falls towards the surface of earth it initially accelerates at what speed?
9.8m/s ^2 due to the force of gravity acting on the object
why may an object have a lower terminal velocity?
if they experience a greater force of friction due to their shape
whats newtons first law of motion
if the resultant force acting on a stationary object is zero, the object will remain stationary,
if resultant force acting on a MOVING object is zero then the object will continue moving in the same direction and same speed ( & velocity)
whats newtons 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
whats inertial mass
a measure of how difficult it is to change the velocity of an object ,, its the ratio of the force needed to accelerate an object over the acceleration produced
an object w/ a large inertial mass will require ______
a larger force to produce a given acceleration than an object w/ a smaller inertial mass
whats newtons third law
when two objects react, the forces they exert are equal in magnitude and opposite in direction
describe the forces acting on a skydiver as he jumps
after jumping the only force is weight due to gravity,, this doesn’t change throughout the journey,, bc of this weight, the skydiver will experience a resultant force acting downwards so will accelerate. As they fall, they experience friction w air molecules (air resistance)… WEIGHT IS GREATER THAN AIR RESISTANCE SO SKYDIVER CONTINUES TO ACCELERATE, as skydivers velocity increases, the air resistance increases,, at a certain point air resistance = weight so theres no resultant force so velocity stays constant (terminal velocity is reached)
describe the forces acting on a skydiver after they release their parachute
the surface area increases so the air resistance massively increases, air resistance is now greater than weight so theres a resultant force acting upwards causing deceleration ,, and decrease in air resistance,, asp the air resistance will = weight so velocity will stay constant so theyre falling at a lower terminal velocity
what is the stopping distance
the total distance travelled from when the driver first spots the obstruction to when the car stops
what is reaction time
the time taken for the driver to spot the obstruction, make a decision and then move their foot to the brake
what is thinking distance
the distance ravelled by the car during the drivers reaction time
what is braking distance
braking distance is the distance the car travels when the driver applies the brakes to when the car stops
what can make reaction time + thinking distance longer
alcohol and drugs, tiredness, distractions eg a phone,
what increases braking distance
wet/icy conditions reduce the friction between tyres and road,, worn tyres reduces friction between tyres and the road ,, worn brakes
what energy changes happen when a car brakes
the kinetic energy is converted into other forms of energy
how does energy change happen when a car brakes
the brake presses against the wheel, the force of friction between the brake and wheel causes kinetic energy to convert to thermal energy causing temp of the brakes to increase,,,, car then slows as it loses kinetic energy
if a car is travelling v fast what does the driver need to apply?
v large braking force which causes car to decelerate rapidly
how does energy change happen when a car brakes with very large braking force ?
the large amount of kinetic energy is transferred to thermal energy causing brakes to overheat and lost control of the car
what is the conservation of momentum
in a closed system, the total momentum before an event is equal to the total momentum after an event
why would a collision between a moving and non moving car cause both cars to move forward at a lower velocity?
the total momentum of the van and the car together is the same as the initial momentum of the van itself
how does shooting a cannonball display the conservation of momentum?
the momentum before firing and the momentum after firing is zero
what do car manufacturers use crash tests for?
to design safety features such as seat belts
what happens to momentum during a crash test
the momentum of the passengers falls from a large amount to zero in less than a second placing huge forces on the passengers that can be lethal
why are safety devices put in place?
to reduce momentum change ie reducing force and risk of serious injury
