linear motion Flashcards
what is linear motion
motion in a straight or curved line
all body parts moving at the same speed in the same direction
what is a scalar quantity
has only magnitude (size)
- speed
- mass
- distance
what is a vector quantity
has both magnitude and direction
- displacement
- velocity
- acceleration
- momentum
- weight
represented by arrows
length of arrow shows magnitude
longer the arrow, bigger the size
direction shown by line of application
what is mass
physical quantity of matter/substance in a body
made of bone, muscle, tissue and fluid
measured in kg
scalar
what is weight
force on a given mass due to gravity
measured in newtons
mass x gravity= weight
gravity on earth is 10 n
vector
what is distance
measured in metres
path a body takes as it moves from the starting to finishing position
what is displacement
measured in metres
shortest route in a straight line between a start and a finsih position
what is speed
scalar
rate of change of a position
speed (m/s)= distance (m) / time (s)
what is velocity
vector
how fast a body travels in a certain direction
rate of change of displacement
velocity = displacement/time
distance time graphs
- line does not go up or down
- no distance travelled. performer is stationary
- constant iagonal direction
- distance run is changing at a constant rate and at the same speed
- curve gets gradually steeper
- more distance covered in a certain amount of time
- performer accelerating
- curve levels off
- less distance covered in a certain amount of time
- performer decelerating
velocity time graphs
- gradient remains constant, indicates performer is travelling at a constant velocity
- gradient gets steeper
- indicates the performer is moving with increasing velocity
- gradient decreases
- performer has decreasing velocity (deceleration)
- as curve goes below the x-axis, this means there has been a change in direction
what is acceleration
- rate of change of velocity
- when velocity increases, positive acceleration occurs
- when velocity decreases, negative acceleration occurs
- acceleration measured in ms^2
acceleration = change in velocity / time
change in velocity = final velocity - initial velocity
what is momentum
- a product of mass and velocity of an object
momentum (kgm/s) = mass x velocity
- vector
what is conservation of momentum
when performer or object is in flight
when in flight neither mass or velocity can be altered
mass is constant (unchanged)
velocity can only be altered by external forces
what is an internal force
generated by the skeletal muscle
what is an external force
comes from outside the body
what are vertical forces
gravity/weight, reaction
weight= gravitational force the earth exerts on our body, pulling us down; greater the mass, greater the weight force pulling down
reaction force= for every action there will be an equal and opposite reaction; always a reaction force when 2 bodies are in contact with eachother
what are horizontal forces
friction and air resistance
static friction= force exerted when there is no motion between 2 surfaces
sliding friction= when 2 bodies in contact have a tendancy to slip and slide over eachother
what is friction affected by
- roughness of the surface
- mass of an object
- temperature of the 2 surfaces- increase in temp reduces friction
what is air resistance dependent on
- velocity of the moving body
- frontal cross sectional area of the moving body
- shape and surface characteristics of the moving body
free body diagrams
- use arrows
- position, direction and length are important
- weight= force drawn down from centre of mass
- reaction= force that starts from when 2 bodies are in contact
- friction= force starts from 2 bodies are in contact and is opposite to the direction of potential slipping
- air resistance= force drawn from the centre of mass opposing the direction of motion of the body
what is a net force
balanced/unbalanced forces
balanced= when 2 or more forces acting on a body equal but opposite
if friction is equal to air resistance, net force is 0
if frictin is greater than AR, acceleration
if frction is less than AR, deceleration
what is impulse
time taken for force to be applied
impulse = force x time
impulse is measured as n.s
if impulse increases so does the rate of change in momentum causing a larger change in velocity
impulse to increase speed
- increase amount of internal muscular force applied
- increase the amount of time in which the force is applied
impulse to decrease speed
- ## increase the time that a force acts on the body/object
force time graphs at start of a race
- positive imoulse bigger than negative = acceleration
force time graphs in teh middle of a race
- positive and negative impulses are equal
- the net impulse is 0
- there is no acceleration or deceleration
- performer is running at constant velocity
force time graphs at the end of a race
- negative impulse is bigger than the positive impulse = deceleration
