Newtons laws of motion Flashcards
motion
movement
force
a push or a pull that alters or tends to alter the state of motion if a body
how can a force make a body move - create motion
- force applied from face of a club head on a golf club onto the golf ball
- golf ball which was stationary is now moving
how can forces make a body slow down or stop
- force applied from hand brakes of a bike
- bike will slow down or stop (due to friction)
how can forces make a body accelerate
- force from feet of runner to starting blocks
- 100 m sprinter pushes of blocks which causes acceleration
how can forces make a body change direction
- force from hand of a volley baller to a volleyball
- volleyball moves in the direction opposite to the direction in which the volleyballer applied the force
how can forces change the shape of a body
- force applied from foot to a football when kicking a ball
- ball changes shape
Newton’s first law of motion is also known as the
law of inertia
N1 - law of inertia
a body will remain at rest or uniform velocity until acted on by an external force
inertia
- resistance of a body to change its state of motion
- (reluctance of a body to start/stop moving)
velocity
rate of motion in a particular direction
give an example of newton’s first law of motion
- sprinter remains stationary in blocks until force is applied to blocks
- once in motion the sprinter will move at constant velocity for the rest of the race until the external forces increase or decrease
- golf ball remains on tee until hit by club
applications - newton’s first law
- at rest net force = 0
- action force at rest = body mass + gravity
- inertia is directly proportional to mass
- positive net force from muscles is required to overcome the inertia
if there’s an increase in fat mass - what happens (N1)
- inertia increases
- increasing reluctance to move
what happens if there’s an increase in muscle mass (N1)
it adds force so increases acceleration
Newtons law of acceleration
- the acceleration of a body is proportional to the size of the force
- acceleration takes place in the direction in which the force is applied
acceleration
the rate of change in velocity /momentum
momentum
the quantity of motion possessed by a moving body
momentum calculation
mass x velocity
what does newton’s second law say that a change in velocity is due to
the force
what must the performer produce to generate a greater acceleration
a greater muscular force
example - newton’s second law
- greater force applied to starting blocks increased acceleration from blocks
- motion is forward in the same direction as force was applied
- momentum can be increased by swinging arms up at the start
applications - newton’s second law
- an increased magnitude of force applied increased acceleration
- the greater the action / reaction force above the mass + gravity the greater the acceleration
- reactive force is opposite to the direction of the action force and takes place in the direction in which the force acts
- acceleration is inversely proportional to mass
newtons law of reaction
- for every action there’s an equal and opposite reaction
action force
the force exerted by the performer on another body
action force example
backward and downward force exerted by a swimmer on the blocks at the start of a race
reactive force
an equal and opposite force to the action force
example reactive force
the forward and upward force exerted by the blocks on the swimmer at the start of the race
example newtons 3rd law
- sprint race start
- performer applies and action force to the blocks and the blocks apply a reaction force back
- causing a change in momentum
- muscular action force applied to the ground results in equal and opposite reactive forces pushing the performer upwards from the ground
action force stationary
mass of person and force of gravity applied to the ground
- a stationary persons weight and gravity force apply an action force to the ground
- an equal and oppose ive reactive force is exerted by the. ground
these forces are equal - what will happen
no motion
for a player to jump of the ground what force needs to be bigger then the weight and gravity force of the player
reaction force / to gain upward acceleration
when jumping why doesn’t the ground move
it has greater inertia
apply newtons 3 laws to a vertical jump - law 1
- to leave the ground the player must exert a greater action force into the ground than their body weight
- therefore the reaction force is greater than weight force
apply newtons 3 laws to vertical jump - law 2
the player accelerated upwards - the greater the force applied to the ground the greater the acceleration upwards and the higher the jump
apply newtons 3 laws to a vertical jump - law 3
the player applies an action force downwards to the ground and the ground exerts an equal and opposite reaction upwards on the player
2 types of forces
- internal
- external
internal force (action force)
- generated by the sports performer with the contraction of skeletal muscle
internal force example
- high jumper contracts their gastrocnemius to plantar flex the ankle and rectus femoris
- this extends the knee to generate the force needed to drive upwards from the ground
external force
comes from outside the body and act upon it
types of external forces
- vertical
- horizontal
vertical forces
weight
reaction
horizontal forces
- friction
- air resistance
weight
the gravitational force/pull that the earth exerts on a body
reaction
the equal and opposite force exerted by a body in response to the action force placed upon it
friction
the force that opposes the motion of 2 solid surfaces in contact
air resistance
the force opposing the motion of a body traveling t though the air
weight - measurement
newtons - N
how does the weight force act on a body
- always present
- acts vertically downwards from COM
- acts in any body on the earths surface
- dependent upon mass of body
- greater mass = greater weight force pulling body downwards
reaction force
equal and opposite force exerted by a body in response to the action force placed upon it
give an example of an action and reaction force
- leg /foot exerts a force on blocks
- blocks exerts a force on the leg / foot
when is a reaction force always present
when 2 bodies are in contact
where are reaction forces present
- in all points of contact
if a reactive force is larger than weight force what happens
body will accelerate upwards
when a reactive force is applied will a greater or smaller mass move more
smaller mass
the greater the difference in mass of the 2 bodies the what in terms of acceleration
further the body with the smaller mass will move
if reaction force and weight force are equal what happens
- forces are balanced
- 0 net force
which direction is reaction force
vertically upwards
what type of force is friction
horizontal
what direction does friction occur in
- opposite to the slipping motion of one solid body over another
if friction is larger than air resistance what will happen
body will accelerate
positive net force
if friction is equal to air resistance what happens
body travels with uniform velocity
0 net force
what factors affect friction
- surface characteristics of 2 bodies in contact with
- roughness of ground surface
- roughness if contact surface
- temperature
- reaction force
surface characteristics
- to increase friction force
- one or more surfaces need to be rough
- e.g athletics
example of a rough ground surface
- athletes run on rubberized track
- increasing friction force
example of a rough contact surface
- sprinters jumpers and throwers west spiked shoes
- maximizes friction force
- causing greater acceleration
temperature - friction
- of 2 surfaces in contact
- if temperature increases
- friction force increases
example of increasing temperature to increase friction
- F1 drivers
- do a warm up lap
- increasing tyre temperature
- increasing friction force
- giving more control when cornering at high speed
increasing normal reaction force - friction
increased friction
example of increasing reaction force to increase friction
- having a higher body mass
- creates an equal and opposite higher reactive force
- increasing friction force with ground
- shotputters: prevents them over rotating and falling out of the circle
how can a cross country runner increase friction
- increase roughness of ground surface
- run in a line on rougher ground track
- increase softness of contact surface by wearing rubber soles in training shoes
what does friction act parallel to
2 surfaces in contact
how does the down force of an object increase friction example
- formula 1
smoother the surface between 2 surfaces in contact how is friction affected
there is less
increasing acceleration
the smaller the surface area between 2 surfaces in contact does what do the friction force
- decreases it
- more acceleration
example of how sprint cyclists are adapted to reduce friction
- race on smooth velodrome track
- have super thin 9mm track cyclist tyres
- less sa on ground
- more acceleration
how are ice hockey players adapted to play using friction
- bigger surface area increased friction so they can change direction , same length blade as boot to increase friction to change direction
how do speed skaters use friction
- thin blade sa
- reduces friction
- allowing increased velocity
- thinner and longer than boot
how is a figure skater use friction to adapt
- blade is thinner and reduced sa
- so they can glide over ice
- toe pick allows them to land safely after leaps and jumps as they can stick it into the ground to increase friction
- gentle curve with toe pick
air resistance - key facts
- shown by horizontal side extending against dom
- acts from com
- acts in opposite direction to motion of body
- force opposing motion of a body is traveling through air
- form of fluid friction
- measured in newtons
factors affecting air resistance
- velocity
- shape
- frontal cross sectional area
- smoothness of surface
- density of air
- mass of body
how does velocity affect ar
- increasing v increases ar
e.g of v on ar
- increased v of track cyclists
- increased ar opposing their motion
how does shape affect ar
- more aerodynamic the shape the lower the ar
example of shape affecting ar
- teardrop is streamlined
- wide at
- front narrow at back
- created a smooth flow around helmet
- e.g spring cyclist
how does frontal cross sectional area affect ar
- lower fsca lower ar
example of fcsa reducing ar
- low crouch position of salon skiers or cyclists
surface smoothness affects ar
- increased smoothness of sa less ar
example of smoothness of surface increasing ar
lycra suits of swimmers
how does air density affect ar
more dense
more ar
example of density of air affecting ar
-misty or foggy air increases ar
- against motion of golf ball decreasing its distance
- higher altitudes lower ar so golf ball goes further
mass of body affecting ar
larger mass
larger inertia
lower ar
example of mass if body affecting ar
- shot put is heavy
- lowering ar
- so it goes further
net force
overall force acting on a body when all other individual forces have been considered
external force
- a force that comes from outside of the body
- horizontal and vertical forces
balanced forces
- when 2 or more forced acting on a body are equal in size but opposite in direction
- body will be stationary or at uniform velocity
- net force is 0
- no change in state of motion
what direction can balanced forces occur in
horizontal
vertical
both
what law do balanced forces refer to
N1- no change in state of motion as there is no net
force present
in an exam q how do we comment on balanced horizontal/vertical forces
- w = r1 + r2
- w + r are equal in size and opposite in direction
- net force = 0
- linked to N1
- no change in motion
- forces are balanced
- will continue at rest or uniform velocity
- w=r
- ar = f
unbalanced forces
- when the force acting in 1 direction is greater in size than the force acting in the opposite direction
- unbalanced forces occur in a vertical horizontal or both directions
- body accelerates or decelerates
- net force = +ve or -ve
- N2 - there is a change in state of motion and a net force is present
what forces only act on projectiles
air resistance
weight
what happens to airborne objects
- they always decelerate
- due to increased ar force
- happens immediately after the force causing it to move is applied
commentary on projectiles and unbalanced forces
- ar is greater than w
- net force is -ve
- body will decelerate
commentary on unbalanced forces
- +ve or -ve net force
- change in motion
- 2 or more forces are unbalanced
- a body will accelerate or decelerate or …
- change direction or shape
- r>w, w>r, ar>f, f>ar
rules when drawing a free body diagram
- use point of application
- show size by arrow length
- direction must be accurate
