Flashcards in Physics paper 2 forces and motion Deck (71):
average speed (m/s)=
change in velocity/time taken
distance time graph what do each sections mean?
3) downhill- going back towards starting point
4) curves= acceleration or deceleration
2) flat=steady speed
3) downhill= deceleration
4) area under curve=distance
5) curve = changing acceleration
what is gravity?
the force of attraction between all masses
what force keeps planets, moons and satellites in their orbits?
what is the orbit a balance between?
the forward motion of the object and the force of gravity pulling it inwards
what is force measured in?
Newtons using a spring balance or newton meter
what is mass measured in
kilograms using a mass balance
mass x gravitational field strength (W= m x g)
give 7 types of force
1)gravity/weight acting straight downwards
2)reaction force from a surface acting upwards
3) electrostatic force- between 2 charged objects
4) thrust-push or pull due to engine speeding it up
5) drag/air resistance/friction slowing things down
6)lift due to an aeroplane wing
7) tension in a rope or cable
what are 3 types of friction?
1) between solid surfaces which are gripping
2) between solid surfaces which are sliding past each other
3) resistance or drag from fluids (liquids or gases)
how do you reduce friction between solid surfaces sliding past each other?
using a lubricant like oil or grease- friction between solids can often cause wear of the two solids in contact
how do you reduce resistance from fluids?
make the shape of object streamlined- lorries and caravans have deflectors on them to make them more streamlined
in a fluid what increases when speed increases?
investigation motion of a toy car experiment-average speed
1)mark a line on the ramp for car to start each time
2)measure distance between each light gate
3) let go of car just before light gate
4)light gate connected to computer so when car passes a beam of light is broken and a time is recorded by date-logging software
5)repeat this experiment to get an average time-reliable
6)using times and distance you can find the cars average speed
what 5 things could you change to investigate the factors that affect the cars motion?
1) changing mass
2)friction-different materials on ramp
3) acceleration-start car higher up on ramp
4) change the angle of the ramp
5) try different cars-size,shape, weight
what is free fall?
when an object is falling with no driving force acting on it
what is in balance in terminal velocity?
how to investigate free fall
using sycamore seeds-small weight and large surface area-reach t.v quickly
1)collect bunch of seeds of diff sizes and measure the mass and wing length of each one. repeat each measurement to make sure it's accurate using ruler. use all the seeds with similar mass but different wing lengths
2) drop each seed from same height and use stopwatch to find how long each one takes to fall to the ground-higher you drop the better-larger measurement and so improves accuracy
4) plot graph-shows bigger wings-larger SA so higher drag. higher drag means lower terminal velocity so slower free fall
what is Newton's first law of motion?
Balanced forces mean no change in velocity
what is Newton's 2nd law of motion?
a resultant force means acceleration- if unbalanced force, the the object will accelerate in that direction
the bigger the force..
the greater the acceleration/deceleration
the bigger the mass..
the smaller the acceleration
the unbalanced force is called ?
the resultant force
mass x acceleration (F=ma)
what affects your stopping distance?
thinking distance and braking distance
what affects thinking distance?
2)how dopey you are- tiredness,drugs,alcohol,old age, inexperience
what affects braking distance?
2)mass of vehicle
3) brake conditions
4) grip-road surfaces/weather conditions/ tyres
what is a moment?
the turning effect of a force
moment is measured in?
force (N) x perpendicular DISTANCE(m) between line of action and pivot
how do you get the maximum moment?
by pushing at right angles(perpendicular) to the pivot because this is longest distance between the line of action and the pivot
what is the point through which the weight of a body acts
the centre of gravity
a freely suspended object will swing until when?
the centre of gravity is vertically below the point of suspension
how can you find the centre of gravity of a shape
1) suspend the shape and a plumb line from the same point
2) draw a line along the plumb line
3) do the same thing again, but suspend the shape from a different pivot point
4)the centre of gravity is where your two lines cross
what does Hooke's law say?
that extension is proportional to force
what is the length of an unstretched metal wire called?
its natural length
when does Hooke's law stop working?
when the force is great enough and has reached its elastic limit-if you increase force past this point the material will be permanently stretched
what material displays elastic behaviour?
when it returns to its original shape once all the forces are removed
what is a galaxy?
a large collection of stars
what is the universe?
a large collection of billions of galaxies
if an object is travelling in circles what happens to its direction?
its constantly changing
how do planets move around the Sun?
in almost circular orbits-slightly elliptical
what are comets?
small lumps of icy rock which orbit the Sun
what type of orbit to comets have?
very elliptical with the Sun at one focus
what are comets periods in relation to Earth?
much longer because they travel from the outer edges of the Solar System
why do comets travel faster when nearer the Sun?
because the increased pull of gravity makes it speed up closer to the Sun
what are the artificial satellites called that have an orbital period of exactly one day?
2 x pii x orbital radius/ time period
What's Newton's third law of motion?
Reaction forces: If object A exerts a force on object B then object B exerts the exact opposite force on object A
What do vector quantities have?
Size and direction
What are some vectors?
Force, velocity, displacement, acceleration, momentum
What are scalar physical qualities?
Have size but not direction
What are some examples of scalar quantities?
Mass, temperature, time, length
What is the resultant force?
Resultant forces refers to the reduction of a system of forces acting on a body to a single force.
How do you work out the resultant force?
choose a direction as the positive e.g north. Add any forces in the north direction and subtract any forces in the south direction
Momentum is measured in?
Mass(kg) x velocity (m/s)
When two objects collide, how do you find the velocity after the collision?
1- choose a positive direction e.g right
2- find total momentum before collision so momentum of object A + momentum of object B
3- find total momentum after collision
- add the object masses x velocity
4- addition of object masses x velocity = total momentum before so rearrange to find v
What do forces cause?
Changes in momentum
What does a larger force do to the momentum?
Means a faster change in momentum and great acceleration
Why do cars have crumple zones?
Crumple on impact, increasing he time taken for the car to stop
What do cars have seat belts?
They stretch slightly, increasing the time taken for the wearer to stop reducing the forces acting on the chest
Why are airbags used?
Slow you down more gradually
Is someone's momentum changes very quickly what happens to the force?
The forces on the body will be very large and more likely to cause injury
How are cars designed
To slow people down over a longer time when they have a crash- the longer it takes for a change in momentum, the smaller the force and so less severe the injuries
Force acting (N) =
Change in momentum (kgm/s) / time taken for change to happen (s)
Total anticlockwise moments =
Total clockwise moments