Science - Physics - Forces- P5 Flashcards
what is a vector quantity ?
magnitude and direction
what is magnitude ?
size
give examples of a vector quantity ?
- force
- velocity
- acceleration
- displacement
- momentum
what is a scalar quantity ?
quantities with magnitude
give examples of scalar quantities ?
- speed
- mass
- time
- temperature
- distance
how are vectors represented ?
as an arrow
what does the length of the arrow show in vectors ?
the magnitude
what does the direction of the arrow show in vectors
the direction of the quantity
what is a force ?
a push, pull or twist on an object that is caused by it interacting with something
what is a contact force ?
where 2 objects have to be touching for a force to act
give examples of contact forces
- friction
- tension
- air resistance
- normal contact force
what is a non - contact force ?
where objects do not need to be touching for the force to act
give examples of non - contact forces
- magnetic force
- gravitational force
- electrostatic force
what is an interaction pair ?
a pair of forces that are equal and opposite, and act on 2 interacting objects
give an example of an interaction pair
earth is attracted to the sun
sun is attracted to the earth
what does gravity do to anything that is attracted to a planet/star - big mass ?
- on the surface of a planet it makes all things accelerate
- it gives everything a weight
what is mass ?
the amount of matter in an object
what is weight ?
the force acting on an object due to gravity
what is the force acting on an object caused by ?
gravitational fields
what does the size of the force acting on an object depend on ?
the gravitational field strength
how does gravitational field strength vary with location ?
the closer you are to the mass causing the field, the stronger it is
what does the weight of an object depend on ?
the strength of the gravitational field at the location of the object
does the objects mass change depending on weather its on the earth or the moon ?
no
does the objects weight change depending on weather its on the earth or the moon
yes
why does an object weigh less on the moon than it does on earth ?
the gravitational field strength on the moon is less
what is weight measured in ?
newtons
is weight or mass a force ?
weight
how is weight measured ?
using a calibrated spring balance, e.g, a newtonmeter
what is mass measured in ?
kilograms, with a mass balance
what is the equation for calculating weight ?
weight = mass x gravitational field strength
how is weight and mass directly proportional ?
if the mass increases, the weight will too, and if the mass doubles, the weight will also double
an object weighs 10 kg on Earth, what is its weight ?
gravitational field strength on Earth = 9.8 N/Kg
98 newtons
what is a resultant force ?
a single force that can replace all the forces acting on an object to give the same effect as the original forces acting all together
a car is driving with a driving (accelerating) force of 1000 N, air resistance of 600 N is acting in the opposite direction, what is the resultant force ?
1000 N - 600 N = 400 N
400 N forwards (accelerating)
what is a free body diagram ?
a diagram that shows all the forces acting on an isolated object , the direction in which the forces are acting on and their magnitudes
how are free body diagrams represented ?
the length of the arrows show the magnitude of the force, the direction the arrow is pointed in shows the direction
what can free body diagrams help you with ?
calculating resultant forces
how do you draw scale drawings ?
- draw all the forces acting on an object
- make sure they’re to scale in the correct directions
- draw a straight line from the start of the first force to the end of the last force, which is the resultant force
- measure the length of this line to find the magnitude
- measure the angle to calculate the direction
what are scale drawings used for ?
finding the resultant force acting on an object
what is equilibrium ?
a state which all forces acting on an object equal zero, so the resultant force is zero
what is a balanced force ?
where the resultant force is zero, as the forces are balanced
what happens to objects that have a balanced resultant force ?
they are either stationary or are moving at a constant speed
how can you resolve a force which acts at awkward angles?
- split it into 2 components at right angles
- Then add the horizontal and vertical components
- use grid lines then measure them
what is work done ?
the energy transferred when a force moves an object through a distance
what is the more simple explanation of work done ?
the energy transferred when a force acts on an object
how do you calculate work done ?
work done = force x distance
1 joule of work is done when a force of 1 newton causes an object to move a distance of 1 metre, so what is equal to what ?
1 joule = 1 newtonmetre
work done and energy transferred are what ?
the same thing
give an example of work done/ an energy transfer question
a brick is pushed along rough ground with a total force of 45 N
the brick moves a distance of 1.4 metres
find total energy transferred
a brick is pushed along rough ground with a total force of 45 N
the brick moves a distance of 1.4 metres
find total energy transferred
force = 45 N
distance = 1.4 M
W = 45 x 1.4
= 63 j
what is work done/ energy transferred measured in ?
joules
what happens if an object has been elastically deformed ?
it can go back to its original shape and length after the force has been removed
what happens if an object has been inelastically deformed ?
it doesn’t return to its original shape and length after the force has been removed
what are elastic objects ?
objects which can be elastically deformed
what is the extension of a stretched spring directly proportional to ?
the load or force applied
what does the spring constant depend on ?
the material you are stretching - a stiffer spring has a greater spring constant
what is the limit of proportionality ?
the limit at which if a spring is stretched too far it won’t return to its original shape
on a graph where is the limit of proportionality ?
where the graph curves
if an object is elastically deformed, what energy is transferred ?
all this energy is transferred to the objects elastic potential energy store
what is elastic potential energy store ?
the energy transferred to the spring as its deformed
how can work done in the elastic potential energy store be found ?
by calculating the area under the linear force-extension graph
when investigating springs using masses, what experiment can you do to check for a fair test ?
check the masses are the same mass and a suitable size
how do you setup the investigating springs using masses experiment ?
- using the spring you are testing load it with masses one at a time up to a total of 5 masses
- using the ruler check that the spring extends by the same amount each time
- if adding one of the masses pushes the spring past its limit of proportionality, use smaller masses and replace the spring
how do you carry out the experiment of investigating springs using masses ?
- using a ruler measure the natural length of the spring at eye level
- add a mass to the spring and allow the spring to come to rest
- measure the springs new length
- record the weight added and work out the extension
- repeat this process recording the total weight attached and calculating the total extension each time until you have enough measurements
what is a moment ?
the turning effect of a force
what is a moment given by ?
force x perpendicular distance from the line of action of the force to the pivot
what is the line of action ?
a straight line passing through the point at which force acts and in the same direction as the force
what is the perpendicular distance ?
the distance along the line that makes a right angle with the line action of the force
if the total anticlockwise moment equals the total clockwise moment about a pivot - what does this mean ?
the object is balanced and won’t turn
what are levers ?
things that make it easier for us to do work
what does the amount of force needed to produce a particular moment depend on ?
the distance the force is applied from the pivot
what do levers do ?
increase the distance from the pivot at which the force is applied so less force is needed for the same moment
why are levers known as force multipliers ?
they reduce the force that is needed to get the same moment by increasing the distance
what are gears ?
circular discs with ‘teeth’ around their edges
what do gears do ?
their teeth interlock so that turning one causes another to turn in the opposite direction, they are used to transmit the rotational effect of a force from one place to another
what can different sized gears be used for ?
to change a moment of a force, a force transmitted to a larger gear will cause a bigger moment as the distance from edge to the pivot is greater
what will a larger gear do ?
turn slower than a smaller gear
give an example on how gears are used ?
bicycles use gears to transmit the turning effect of the pedals to the back wheel- you can change gear to alter the ratio between how fast you pedal and how fast the wheels turn
what is pressure ?
the force per unit area
what are fluids ?
substances that can flow because their particles are able to move around, either a liquid or gas
what is the unit for pressure ?
pascals Pa
what is density ?
a measure of how close together the particles in a substance are
what is density like in liquids ?
uniform, and doesn’t vary in shape or size
what will a denser liquid have ?
more particles in a given volume
how does pressure increase with density in liquids ?
if a liquid is denser there are more particles to collide so there are more collisions so a higher total force is exerted and there is a higher pressure
what can affect pressure in a liquid ?
depth
what happens when depth increases ?
the number of particles above a point increases, so the weight of these particles add to the pressure experienced at that point so liquid pressure increases with depth
how can you show how pressure in liquid increases with depth ?
- use a tube with equally sized holes cut into the edge of it
- when the tube is filled with water the pressure is greatest at the bottom
- so at the bottom hole, the water spurting out travels faster than the water spurting out at the top
what is the atmosphere ?
a layer of air which surrounds earth
how is atmospheric pressure created ?
on a surface by air molecules colliding with the surface
as altitude increases, what happens to atmospheric pressure ?
it decreases
why does atmospheric pressure decrease with altitude ?
- as altitude increases air gets less dense so there are fewer air molecules in the air to collide with a surface
- with increasing altitude there are fewer air molecules so the weight of the air above decreases
when an object is submerged fully in an object, where is force exerted ?
in every direction
as pressure increases with depth, what happens ?
the force exerted on the bottom of the object is larger than the force acting on top of the object which causes a resultant force called upthrust
what is upthrust equal to ?
the weight of fluid that has been displaced
if the upthrust of an object is equal to an objects weight, what happens ?
the forces balance and the object floats
if an object weight is more than the upthrust what happens ?
the object sinks
why does whether or not an object floats depends on its density if the object is less dense than the fluid its placed in ?
- an object less dense than the fluid its placed in weighs less than the equivalent volume of the fluid so it displaces a volume of fluid that is equal to its weight before it can become completely submerged ,at this point upthrust is equal to the objects weight so the object floats
why does whether or not the object floats depend on its density if the object is more dense than the fluid it is placed in ?
- an object that is denser than the fluid it is placed in weighs more than the equivalent volume of fluid so it is unable to displace enough fluid equal to its weight so it weighs larger than the upthrust so it sinks
how do submarines use upthrust ?
- to sink large tanks are filled with water
- this increases the weight of the submarine so that its weight is more than the upthrust
- to rise to the surface the water is expelled and the tanks are filled with air to reduce the weight so that its less to the upthrust
what is displacement ?
a vector quantity which measures the distance and direction in a straight line from an objects strating point to its finishing point
what is speed ?
how fast you are going with no regard to direction
what is velocity ?
how fast you’re going and in which direction
what happens to an object that is moving in a circle ?
it can have a constant speed but always a changing velocity
what is the average walking speed ?
1.5 m/s
what is the average running speed ?
3 m/s
what is the average cycling speed ?
6 m/s
what is the average car speed ?
25 m/s
what is the average train speed ?
55 m/s
what is the average plane speed ?
250 m/s
what can affect speed ?
fitness
age
terrain
what can the speed of wind be affected by ?
change in termperature
atmospheric pressure
large structures
what can the speed of sound be affected by ?
what the sound waves are travelling though
how do you measure the speed of an object ?
time how long it takes to travel a certain distance
what is acceleration ?
how quickly the velocity is changing
what can cause a change in velocity ?
change in speed or direction
what is acceleration measured in ?
m/s squared
what will the velocity be if an object is slowing down ?
it will be negative = negative acceleration = deceleration
what is constant acceleration known as ?
uniform acceleration
give an example of uniform acceleration ?
acceleration due to gravity
what are distance time graphs ?
a way of describing the motion of something travelling in a straight line
what does the gradient of a distance time graph tell you ?
how fast your object is travelling
what does a gradient = in a dtg
speed
dtg - straight uphill section =
travelling at a steady speed
dtg - steeper the graph =
faster it is going
dtg - flat sections =
stationary
dtg - curves =
acceleraton
dtg - steepening curve =
accelerating
dtg - leveling of curve =
decelerating
how can you calculate the speed of an object at a point if it is changing speed ?
find a tanget of the point, work out gradient
what is a velocity time graph used for ?
to show an objects motion
what is the change in an objects velocity over time ?
acceleration
what does the gradient of a velocity time graph tell you about ?
acceleration
vtg - gradient =
objects acceleration
vtg - flat sections =
steady speed
vtg - steeper the graph =
greater the acceleration/deceleration
vtg - uphill =
acceleration
vtg - downhill =
deceleration
vtg - curve =
changing acceleration
how can acceleration be found on a velocity time graph ?
calculating the gradient
how is distance travelled found on a velocity time graph ?
equal to the area under the graph
why will an object always slow down if it is has no force propelling along it ?
because of friction
what direction does friction act in in terms of movement ?
the opposite direction to movement
how do you travel at a steady speed ?
the driving force needs to balance the frictional force
when do you get friction ?
between 2 surfaces in contact or when an object passes through a liquid
what is drag ?
something that causes resistive forces
how do you reduce drag in fluids ?
by keeping the shape of the object streamlined
what is a streamlined object ?
an object which allows fluids to flow over it easily so they don’t slow down the object as much as it passes through them
give an example of something streamlined
a sports car - moves through air with little movement so it can use less driving force with the same speed compared to other vehicles such as vans
what do frictional forces from fluids always increase with ?
speed
how do you increase the speed of a vehicle ?
- reducing drag by changing the shape of a vehicle to make it more streamlined
- increasing the power of the vehicles engine so the driving force becomes larger and so the drag force on the vehicle will equal the driving force at a higher speed
what is terminal velocity ?
the maximum velocity of a falling object can reach without any driving forces, the velocity at which the resistive forces acting on the object match the force due to gravity
when a falling object falls through a very large distance what happens, how does terminal velocity work ?
gravity is greater than the frictional force slowing it down so it accelerates
as the object moves faster frictional forces increase
this gradually reduces acceleration until the frictional force is equal to the accelerating force then the object will no longer accelerate
an object has reached its maximum speed, terminal velocity
describe a velocity time graph for a falling object
- starts with a steep gradient
- gradually becomes less steep
- becomes flat
what affects terminal velocity ?
- shape
- area
- air resistance causes things to fall at different speeds
- an objects drag compared to weight
what is Newtons first law ?
a resultant force is needed to make something start moving, speed up, or slow down, or change direction
what happens to the object if the resultant force is 0 ?
the object will remain stationary
if the resultant force on a moving object is 0, what happens ?
it will carry on moving at the same velocity
if an object is moving at a constant velocity, what do the forces have to be ?
balanced
if there’s a non - zero resultant force acting on the object, what will happen ?
its velocity will change in the direction of the force
when a resultant force acts on an object, what are the different forms in which the object will experience the change in velocity ?
- starting
- stopping
- changing direction
- speeding up
- slowing down
what is Newtons 2nd law ?
- the larger the resultant force acting on an object, the more the object accelerates - force and acceleration are directly proportional
- acceleration is inversely proportional to the mass of the object - an object with a larger mass accelerates less than one with a smaller mass
what is inertia ?
the tendency to continue in the same state of motion ( to continue moving at the same velocity )
what is an objects inertial mass ?
measures how difficult it is to change the velocity of the object
how do you set up the investigating motion practical ?
- set apparatus up
- trolley should hold a piece of card in the middle that will interrupt the signal on the light gate twice
- measure the length of each bit of card that will pass through the light gate and input this into the software, the light gate can measure velocity for each bit of card
- connect the trolley to a piece of string that goes over a pulley and is connected on the other side to a hook
- mark a starting line on the table the trolley is on and place the trolley so its front end is lined up with it
- make sure string and table are the right length so that your trolley passes through the light gate before masses hit the floor or the trolley hits the pulley otherwise the accelerating force will have been removed
in the investigating motion practical light gate is used, what is light gate ?
an arch shaped piece of equipment which sends a beam of light from one side of the arch to the other. when something passes through the lightgate it interrupts the beam of light , when used with a data logger the light gate can detect interruption and measure how long the interruption lasted
what can the software used to detect the interruption of light on the light gate also do ?
work out the acceleration of the trolley by working out the difference between the 2 velocities it has measured and by using the time that has passed between the 1st and 2nd interruptions of the light gate signal
in the investigating motion practical, what do the masses attached to the hook do ?
provide an accelerating force that causes the trolley to move when released
how do you carry out the investigating motion practical ?
- hold the trolley so the string is horizontal and taut
- release the trolley and record the acceleration measured by the light gate as the trolley passes through it
- this is the acceleration of the whole system
- ## repeat for a more accurate result
how do you change the investigating motion practical if you want to see if mass changes acceleration ?
vary the masses by adding one each time to the trolley record your results each time you add a mass
how do you change the investigating motion practical if you want to see how force changes acceleration ?
keep the total mass of the system the same, but add masses to the hook by transferring masses to the hook each time this will increase the accelerating force while keeping the mas of the system the same
by adding masses to the trolley, what happens ?
decreased acceleration of the trolley
by transferring masses from the trolley to the hook what happens ?
acceleration increases
what is Newtons 3rd law ?
when 2 objects interact, the forces they exert on each other are equal and opposite
give an example of Newtons 3rd law
when you push a shopping trolley, the trolley will push back against you just as hard
what is an emergency stop ?
where the maximum force is applied by the brakes in order to stop the car in the shortest possible distance
the longer it takes to perform an emergency stop, the what ?
higher the risk into crashing into whoevers in front
what is the total stopping distance of a vehicle ?
the distance covered in the time between the driver first spotting the hazard and the vehicle coming to a complete stop
what determines stopping distance ?
thinking distance
braking distance
what is thinking distance ?
the distance the vehicle travels during the drivers reaction time
what is braking distance ?
the distance the vehicle stops after the brakes are applied until it comes to a complete stop
what affects thinking distance ?
- how fast your going
- your reaction time
what affects braking distance ?
- how fast your going
- how good your brakes are
- how good the tyres are
- how good the grip is (weather)
what is reaction time affected by ?
tiredness
drugs
alcohol
lack of concentration
what is a typical reaction time between ?
0.2 and 0.9
why does the quality of your brakes affect braking distance ?
worn or faulty brakes won’t be able to apply as much force as well maintained brakes
why does the quality of your tyres affect braking distance ?
tyres should have a minimum tread depth of 1.6 mm
in wet conditions tread patterns helps to stop water from getting trapped between the tyres and the road and provides a channel through which the water can escape
why does how good the grip is affect braking distance ?
water, ice, leaves, muck on the road can increase braking distance as they can result in reduced friction between the tyres and the road so you travel further before stopping and may skid
what are the thinking and braking distances typically for a car travelling at 30 mph ?
thinking - 9m
braking - 14 m
what are the thinking and braking distances typically for a car travelling at 50 mph ?
thinking - 15 m
braking - 38 m
what are the thinking and braking distances typically for a car travelling at 70 mph ?
thinking - 21 m
braking - 75 m
how do drivers avoid car accidents ?
drovers leave space between the car and the one in front of them
speed limits
why does speed affect braking distance more than thinking distance ?
thinking time and speed are directly proportional as thinking time is constant, but the higher the speed the more distance you cover
braking distance is faster the more you speed up, if speed doubles, braking distance squares because when a vehicle brakes work done must be done to transfer energy away from the vehicles kinetic energy store
what would a graph between thinking distance and speed be ?
linear - straight line
what would a graph between braking distance and speed be ?
curved - as it increases with the square of the scale
give a way to measure reaction time ?
use a computer based test
describe the ruler drop test ?
- sit with your arm resting against the edge of the table
- get someone else to hold a ruler so it hangs between your thumb and forefinger lined up with 0
- without giving warning, the person holding the ruler randomly drops it
- as soon as possible other person catches the ruler with their thumb and forefinger as quickly as possible
- the measurement on the ruler at the point where it is caught is how long it took you to react, he bigger the number = slower reaction time
how can you improve the ruler drop test ?
- repeat it lots
- add a blob of modelling clay at the bottom of the ruler so it falls in a straight line
- use the same person to drop the ruler, and the same person to catch it
- introduce distracting factors such as music, tv to see how that affects reaction time to compare
what does braking rely on ?
friction between the brakes and the wheels
what happens when the brake pedal is pushed ?
the brake pads are pressed onto the wheels causing friction, causing work to be done
this transfers energy from the kinetic energy stores of the wheels to thermal energy stores of the brakes
so the temperature of the brakes increase
the faster the vehicle is going the more kinetic energy it has so the more work done the vehicle needs to stop what does this mean about the braking force ?
it needs to have a greater force to stop it within a certain distance
what does a larger braking force mean ?
larger deceleration
what does large deceleration mean ?
lots of work is done so lots of energy is transferred to thermal energy stores and brakes become very hot - which can cause them to stop working
what is momentum ?
a property of a moving object that is a product of its mass and velocity
the greater the mass of an object and the greater its velocity, the greater the ….
momentum
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, e.g, an explosion
if the momentum before an event is 0, what is its momentum after an event ?
0
-when a velocity changes, what happens to the momentum ?
it changes
if the force acting is larger, what will happen to the momentum ?
there is a faster change in momentum
the longer it takes for a change in momentum, the smaller the what ?
rate of change of momentum and so the smaller the force
what safety features are in cars to reduce momentum ?
- crumple zones
- seat belts
- air bags
- bike helmets
- crash mats
what are crumple zones ?
parts of the cars bodywork that are designed to crumple on impact increasing the time taken for the car to stop
how do seat belts reduce momentum ?
they stretch slightly, increasing the time taken for the wearer to stop
what are air bag and how do they reduce momentum ?
inflate during a collision so you hit the airbag instead of the dashboard and the compressing air inside it slows you down more gradually
how do bike helmets help during a crash ?
contain a crushable layer of foam which lengthens time taken for your head to come to a stop if you crash, educing impact on your brain
how do crash mats help reduce momentum ?
increases the time for you to stop if you fall or land on them as they are made of soft and compressible materials
