Forces CGP Flashcards
what is scalar quantity
what is vector quantity
5 examples of each
magnitude only
magnitude + direction
scalar– speed, distance, mass, temp,time,
Vector-force,velocity,displacement,acceleration,momentum
what is a force
eg of contact force x4
eg of non contact forcex3
what is an interaction pair
push/pull that acts on object due to interaction w/ another object
.
friction, air resistance, tension in rope,normal contact
magnetic,gravitational, electrostatic
.
-pair of forces that r equal + opposite. Act on 2 interacting objects (3rd Law)
the unit for force
a contact force is when
a non contact force is when-
N
objects physically touching
objects physically separated
what is gravitational force
what does gravity attract
2 effects of gravity
.
is it vector/scalar
force of attraction btwn masses
all masses
-makes everything fall to the ground on surface of planet
-gives everything weight
-vector
what happens when a force causes object to move through a distance
describe energy transfer involved when work is done
work is done on the object (energy transferred)
-to make object move, force must be applied
-thing applying force needs energy source
-the force does ‘work’ to move object, energy transferred from one source to another
-work is done whether energy transferred usefully/wasted
work done + energy transferred are the same thing
what is mass
what is weight
.
What is the force acting on an object on earth caused by
when does gravitational field strength increase
-mass-amount of ‘stuff’ in object, stays same
-weight-force acting on object due to gravity(the pull of gravitational force
-gravitational field strength around earth
-closer to mass causing field
-stronger for larger masses
-weight of object affected by
-where does the weight of an object act from
-Describe this for an object with same density throughout- Uniform object
-what is used to measure weight
-what is used to measure mass
-Briefly describe relationship btwn mass + weight
gravitational field strength at point where object is
-single point, centre of mass
-centre of object
.
-Newtonmeter (calibrated spring balance)
-mass balance
-directly proportional
Weight= Mass x Gravitational field strength
units for each
what happens if you double the mass of object
weight- N
mass- Kg
Gfs- N/Kg
weight doubles
what do sizes + arrows in free body diagrams show
where do the arrows come from
magnitude of forces + direction
centre of object
work done =force x distance
state units
Work done- J(oules)
Force- N(ewtons)
Distance- m
-one joule of work is done when
- 1 Joule=
force of 1 newton makes object move by 1 metre
1 Joule= 1 newton-metre
why do you need more than one force to stretch/compress/bend an object
-Work is done (energy is transferred) when a force stretches/compresses an object. How.
-what is elastic deformation
-what is inelastic deformation-
-what happens to the energy transferred to an object if it is elastically deformed
otherwise object would just move in direction of applied force
-forces also should be balanced
energy transferred to the elastic potential energy store of the object
-can go back to og shape + length when force removed
.
-doesn’t return to og shape + length once force removed
.
.
-ALL the energy goes to its elastic potential store
Force= spring constant x extension
state units and what extension means
-what does spring constant depend on
.
F- Newtons
spring constant- N/m
Extension- m
extension can be extension or how much an objects been compressed
-spring constant depends on stiffness of material, stiffer material has greater spring constant
what is the relationship btwn force and extension
.
-work done on the spring and elastic potential energy stored are = if
-the extension of an elastic object is …… to force applied if….
direct proportion
-spring has not inelastically deformed
-directly proportional if limit of proportionality has not been reached
what is limit of proportionality
maximum force , above it the extension is not proportional to force.
where graph curves down on force-extension graph OR curves up on extension-force graphs
describe rp investigating springs
.
.
.
.
.
.
.
.
how would you work out weight of stone
-work out weight of masses using W=mg
-add pointer eg wooden splint to bottom of spring and top of spring on 0
-measure unstretched length of spring w/ metre ruler clamped to stand-( eye level )
-Add 1N weight, let spring come to rest. read position of pointer
-repeat 6 times - increasing masses
-work out extension caused: og length - each new length
-plot on graph- Force on y axis / extension on x axis
-
-measure ext. of spring when stone hangs
-read weight off from graph
what does it mean when the line of best fit is straight in force-extension graph
-how would you work out K ( spring constant) in this scenario
.
-what does it mean if graph curves
-gradient of line is k as Force= spring constant x extension
.
-limit of proportionality reached- the spring stretches at uneven rate, more each time, even though same mass is added each time
Elastic potential energy= 0.5 x spring constant x (extension)”2
-what can u use this to work out
-elastic potential energy (j) in elastic deformation means 2 things-
.
-area under graph in force-extension graph =
.
-work done in stretching /compressing string (if limit of proportionality not reached)
-energy stored in spring
-energy transferred to spring as its deformed/ by string when returns to og shape
-the elastic potential energy store of stretched spring
what causes an object to rotate
what is a moment
Moment=forcexdistance
state units
-what distance is used
a force/system of forces
the turning effect of a force
moment- Nm
force- N
distance- m
-ALWAYS use distance perpendicular from the pivot to the line of action of the force
how do you get the maximum moment/turning effect when using a spanner
-why
-how can you increase moment
push at right angles to the spanner
-pushing at any other angle means smaller smaller distance so smaller moment
-larger force or longer perpendicular distance
how do you know if an object is balanced
-what equation do you use to find an unknown moment in a balanced object
total clockwise moment about a pivot= total anticlockwise motion about that pivot
-same equation as normal moment
what do levers do
-what do gears do
-what does turning one gear that is interlocked w/ another cause
-how do you increase the moment of a force in a gear / lever
a large …. will turn ……. than a small one
increase distance from the pivot at which the force is applied- reduces the force needed to get the same moment bcse moment=forcexdistance
-transmit rotational effect of a force from one place to another
-next gear turns in other direction
-use larger gear/ longer leaver
-large gear will turn slower than a small one
in physics a fluid is…
what does the pressure in fluids do
*how come particles in fluids exert
pressure
Pressure=Force/ Area
state units
liquid/gas
-exerts a force normal (at right angles) to any surface
-particles have mass and exert a force when they collide w/ an object
Pressure is force per unit area so particles exert pressure
Pressure- Pa
Force- Newtons
Area- m SQUARED
why in a liquid does the pressure at a point increase with the height of the liquid above that point 4 points
pressure = height of column x density of liquid x gravitational field strength
state units
-the density in a liquid is the same throughout.
-the more dense it is the more particle collisions so higher pressure
-as depth increases, no. of particles above the point increases.
-the weight of these particles causes pressure to the point
Pressure- pa
Height of liquid- m
density- KG/mCUBED
gravitational field strength- N/kg
what is upthrust 3points
if an object is submerged in water, what is the upthrust acting on the object equal to
a submerged object experiences greater pressure on bottom of its surface than on top.
this creates a resultant force upwards.
this is upthrust
-the weight of water that’s been displaced
whether or not an object floats depends on
when does object float
when does object sink
describe why an apple would float in water-
describe why will potato sink in water-
objects density
-if upthrust on object equal to objects weight
-if weight of object is more than the upthrust acting on object
-apple is less dense than water. this means it weighs less than the equivalent volume of water. apple displaces a volume of water equal to its weight before it completely submerges . it will float at that level
-potato denser than water.
cant displace enough water to equal its weight.
Its weight is always larger than upthrust.
it sinks
what is the atmosphere
how does atmosphere get less dense
how is atmospheric pressure created
-why does atmospheric pressure decrease as altitude increases - 4 points
-a thin layer (relative to the size of the Earth) of air round the Earth
-with increasing altitude
-air molecules collide with a surface
-atmosphere gets less dense,
-fewer air molecules to collide w/ a surface
-and weight of air decreases
-so less pressure as there’s less air
what is displacement
what is speed
what is velocity
distance= speed x time
give units
-distance+ direction in straight line from start to finish point
-how fast
-speed in a given direction
distance- m
speed- m/s
time- s
what should you remember about speed of a moving object-
speeds for:
person walking
person running
person cycling
car
train
plane
sound in air
speed of a moving object is rarely constant
1.5 m/s
3 m/s
6 m/s
25 m/s
55 m/s
250 m/s
330 m/s
what affects speed x4
what can affect wind speed x3
age,
terrain,
fitness
distance travelled
-temp
-atmospheric pressure
-buildings/structures
what is acceleration
acceleration= change in velocity / time
state units
*if you have to use an estimate how long it takes a car to stop do ~1 second
-what is uniform acceleration
rate of change of velocity
acceleration- m/sSQUARED
velocity- m/s
time- s
-constant acceleration
how does the motion in a circle have constant speed but changing velocity
This is using UNIFORM ACCELERATION:
(final velocity)¬2 - (initial velocity)¬2
= 2 x acceleration x distance
state units
what is the approximate acceleration on earth of a free falling object in uniform(constant) acceleration
the speed stays the same but constantly changing direction therefore velocity is always changing but speed isnt, eg a car on roundabout
velocity- m/s
acceleration- m/sSQUARED
distance- m
9.8 m/sSQUARED
DISTANCE TIME GRAPHS
what is it used for
what do these mean:
gradient
flat
straight uphill section
curves
steepening curve
levelling off curve
gradient of a tangent
object travelling in straight like
gradient=speed
flat=stopped
straight uphill section=steady speed
curves= acceleration/deceleration
steepening curve=speeding up
levelling off curve=slowing down
gradient of a tangent=speed
VELOCITY TIME GRAPHS
what does it show
what do these mean:
gradient
flat
graph gets steeper
straight uphill, downhill lines
curve
area under graph
how objects velocity changes as it travels
gradient=acceleration
flat=steady speed
gets steeper=greater acceleration/deceleration
uphill/downhill= acceleration/deceleration
curve=changing acceleration
area under graph= distance travelled
-what happens is object has no force pushing it
-what direction does friction work in
-How do you travel at steady speed
-2 scenarios friction can happen
-what is drag
-an example of drag
-slow down + stop due to friction
-opposite direction to movement
-driving force needs to balance friction
Friction:
2 surfaces in contact
object passes through liquid (drag)
-drag- the resistance you get in a fluid (gas/liquid)
-air resistance
how can you reduce drag
what does terminal velocity depend on-
what is terminal velocity determined by
-keep object streamlined- lets fluid flow easily across it
-move at slower speed- reduces friction
-shape. area
-drag in comparison to weight
describe how person falling through air reaches terminal velocity - 3 stages
-resultant force is gravity which acts downwards
skydiver accelerates downwards
-speed increases so air resistance increases but resultant force is still gravity
skydiver has a slower acceleration downwards
-eventually force of gravity and air resistance are =
skydiver experiences no acceleration and falls at steady speed- TERMINAL VELOCITY
why would hammer + feather fall at same rate on moon
what changes in a skydivers fall with open parachute
no air - no air resistance so accelerating force acts the same on any object
more air resistance, same weight
terminal velocity lowered eg 15mps
what is newtons first law
what does this mean for a car at steady speed
when will velocity of an object change
If the resultant force on STATIONARY object is 0, the object will REMAIN stationary
If resultant force on MOVING object is 0 it’ll move at same VELOCITY
-the resistive and driving forces are balanced
-velocity will change if there is a resultant force
what are the different form of ‘acceleration’, when there is a resultant force
Newtons second law:
as words-
as an equation-
stopping,starting,slowing,speeding,changing direction
acceleration of an object is proportional to resultant force and inversely proportional to mass of the object.
F=ma
Resultant force (N)=acceleration x mass
what is inertia mass a measure of
define inertia mass
what is the equation for inertia mass
the measure of how difficult it is to change velocity of an object
-the ratio of force over acceleration
-same equation as 2nd law, rearranged.
m= F/a
newtons third law
a book is resting on a table in equilibrium. there are TWO pairs of forces in this situation that abide Newtons 3rd law.
What are they
Whenever two objects interact, the forces they exert on each other are equal and opposite.
1) weight of the book is pulled down by gravity from earth
the book also pulls back up on the earth
2) the normal contact force from the table pushes up on the book
the normal contact force from the book pushes down on the table
describe a contact force of a chair and the ground
chair exerts force on the ground
ground pushes back/up w/ same force (the normal contact force) Equal but opposite forces are felt by chair and ground
what does the gravitational force do- non contact force
attracts all objects to other objects
sun and earth are attracted to each other by gravitational force
an equal but opposite force of attraction is felt by the sun and earth
what is the electrostatic force
magnetic force-
what is happening in tug of war-contact force
what is happening when sky diver falls through air- contact force
force btwn 2 charged objects
force experienced by an object when in a magnetic field
force of tension in rope is pulling on person
sky diver falls, air particles collide w/ parachute, force of air resistance acts upwards
unit for weight
is weight vector/scalar
is mass vector/scalar
N
-scalar
what are the energy transfers taking place when car brakes
brake presses against wheel and friction acts
ke of car —> thermal energy store of brakes
temp of brakes ^ . Car slows down as it loses Ke
what are the energy transfers when person pushes object against the carpet
thermal energy store in muscles goes to ke store of object but also to thermal energy store of object due to friction
force has done work on an object when…
he force causes displacement of the object
