explaining motion Flashcards
what does velocity tell you about an object?
- speed
- direction of travel
idea of distance:
opposite direction = negative
changes in distance in 1 direction = positive
what do you need to know to calculate an objects speed?
- distance
- time
how do you calculate speed?
s x t
what is instantaneous speed?
speed of an object at a particular point in time
what 2 things of a distance time graph is a measure of the speed?
slope or gradient
steeper the slope, greater speed
how can you calculate the speed of an object?
working out gradient of a displacement time graph:
what is the instantaneous velocity?
speed together with an indication of direction
what happens in a curvy distance time graph?
curved, speed changing
what does a speed time graph show?
slope or gradient represents how quickly accelerating
steeper slope, faster speed increase
why are speed time graphs used in lorry tachographs?
- don’t exceed speed limit
- rest for suitable amounts of time
what are velocity time graphs?
quantity velocity has both speed and direction, change in either will cause change in velocity
a velocity time graph can have negative values for the velocity axis
how can you calculate acceleration?
acceleration = change in speed/time taken
what is a force?
2 objects interacting with each other
whenever 1 object exerts a force on another, experiences a force in return
what are forces in an interaction pair?
- equal in size
- opposite in direction and act on diff objects
what are some examples of forces?
gravity (weight):
- 2 masses attracted to each other
air resistance (drag): - air slows down skydiver by pushing upwards against him
rocket and engines:
- engine pushes gas back (action) + gas pushes rocket forward (reaction)
what happens when an object is resting on a surface?
object pulled down onto surface by gravity
- surface pushes up on object with an equal force
called reaction of the surface
what is friction?
when 2 objects try to slide past one another both objects experience a force that tries to stop them from moving
objects don’t have to moving to experience friction eg friction from car brakes stops it from rolling
why are arrows used when drawing diagrams of forces?
- size of arrow represents size of force
- direction of arrow shows the direction of force
what happens if more than 1 force acts on an object?
will…
- add up if acting in same direction
- subtract if acting in opposite direction
overall effect of adding or subtracting forces called resultant force
what is momentum?
measure of the motion of an object
how can you calculate momentum?
momentum = mass x velocity
if lorry and car travelling at same speed, lorry will have more momentum bc bigger mass
if the resultant force acting on an object is 0, it’s momentum won’t change, so what is the object?
- stationary
- already moving, continue moving at a steady speed
if the resultant force acting on an object is not 0, is causes a change of momentum in the direction of the force which could what?
- make a stationary object move
- increase/decrease speed of object
- change objects direction
what does change in momentum depend on?
- size of resultant force
- length of time the force is acting on the object
what do collisions do and what can they affect?
cause changes in an objects momentum
can affect:
- car
- passengers = injuries
what are safety devices?
force of the impact on human body can be reduced by increasing time of the impact
purpose of..
- seat belts
- crumple zones
- air bags
what do cars and bicycles have?
- driving force:
produced by engine or energy of cyclist - counter force:
caused by friction
what happens if the driving force is bigger, equal to, or smaller than the counter force?
bigger:
vehicle speeds up
equal to:
constant speed
smaller:
slows down
what is kinetic energy?
moving object has kinetic energy
depends on:
- mass
- velocity
greater mass and velocity, more kinetic energy
how can you calculate kinetic energy?
1/2 x mass x velocity2
