Forces Flashcards
what does the weight of an object depend on?
gravitational field strength & location of object within gravitational field
what is a resultant force?
single force acting in one direction from adding or subtracting more than one force in different directions
how do you find the resultant force of 2 forces using a scale diagram?
tip to tail method
put the scale
measure the direction as a bearing
how do you find the missing force for an object in equilibrium using a scale diagram?
the scale diagram should form a triangle because the resultant force is 0
tip to tail method - connect the triangle
put the scale
measure the direction as a bearing
what is elastic potential energy?
energy transferred to the spring as it is deformed
what do levers & gears do?
multiply the effect of a turning force using moments
why is density constant in a liquid?
it does not change with the shape or size of the container
what does a submerged object experience?
the pressure of the fluid
what volume of liquid does an object displace when it floats?
volume equal to its weight
what happens to atmospheric pressure as altitude increases & why?
atmospheric pressure decreases
number of air particles & weight of air above a surface decreases because density decreases
as height increases there is always less air above a surface than at a lower height
what is atmospheric pressure caused by?
air particles colliding with a surface
what is the typical speed of cycling?
6m/s
what is the typical speed of a car?
25m/s
describe the acceleration of an object falling through a fluid
the object initially accelerates due to the force of gravity (because the force of gravity is much greater than the frictional force slowing it down)
as its speed increases, frictional force increases
this reduces acceleration until frictional force = accelerating force
so resultant force will be 0
so the object moves at its terminal velocity
explain the shape of a velocity-time graph for a skydiver
when an object first sets off, the gravitational force in much higher than the frictional force so accelerate quickly
as speed increases, frictional force increases
so rate of acceleration decreases
until accelerating force = frictional force so resultant force is 0
skydiver has reached terminal velocity - maximum speed & stay at constant speed
what is newton’s first law?
if the resultant force is zero, a stationary object will stay stationary & a moving object will continue moving at constant velocity (same speed & direction)
what is inertia?
the tendency for an object to stay in a state of rest or uniform/constant motion
what is newton’s second law?
force is directly proportional to acceleration
F=ma
how do brakes work?
brake pads are pressed against tyres, causing friction, which causes work to be done
this transfers energy from kinetic energy store of car to thermal energy store of brakes so brakes increase in temperature
what can a large deceleration cause?
brakes to overheat & skidding
= injury
how do you estimate the braking force involved in deceleration of vehicle?
assume deceleration is uniform so use v2-u2=2as to find deceleration (a)
use F=ma with m=1000kg (estimate of mass of car)
how does speed affect braking distance?
work done to stop the car = car’s kinetic energy store
E=1/2mv2
as speed doubles, kinetic energy increases 4-fold
so work done to stop car increases 4-fold
W=Fs so braking distance increases 4-fold
