5- FORCES Flashcards
what are vector quantities, give examples, how are vectors represented
what are scalar quantities, give examples
vector quantities-magnitude and direction (force,velocity,displacement, acceleration,momentum)
scalar - magnitude , no direction
(speed distance, mass, temperature, time)
how are vectors shown
arrow
length shows magnitude
directin shows direction of quantity
(same speed=same lenght, different velocities due to different directions)
what is a force
push or pull on object that is caused by it interacting with something
when two objects interact , the force is produced on both objects
what is a contact force
two objects have to be touching for a force to act e.g. friction, air resistance, tension in ropes, normal contact force
non contact force
object does not need to be touching for the force to act e.g. magnetic force, gravitational, electrostatic
what is an interaction pair
a pair of forces that are equal and opposite and act on 2 interacting objects
explain how sun and earth are attracted
by gravitational force, non contact- equal and opposite force of attraction is felt by both sun and earth
explain how a chair stays on ground
chair exerts force on ground, ground pushes back at chair with same force - normal contact force.
equal but opposite felt by chair and groudn
gravitational force
force of attraction between masses- causes everything to fall to ground and gives everything a weight
weight
mass(kg )x gravitationalfield strength(N/kg)
force acting on object due to gravity - the pull of graviational force on object, force caused by gravitational field around earth-
measured in newtons with newtonmeter or calibrated spring balance
weight depends on strength of graviational field at location of object - changes with location
mass and weight are directly proportional
gravitational field strength
varies with location, it is stronger the closer you are to the mass causing the field . it is stronger for larger masses
e,g, something will weigh less on moon than it does on earth
resultant force
and how do you calculate it
overall force on a point or object-if a number of forces are acting at a single point - you can replace with a single force
if all forces are acting on same line (parallel ) resultant is found by :
adding those going in same direction - any going in opposite direction = resultant force
how is work done & energy transferred when a resultant force moves an object through a distance
1- to make thing move:force must be applied 2- what applies force needs source of energy like fuel/food
3-force does work& energy is transferred from one store to other
(e.g. when pushing object on rough surface, work is done against frictional force, energy goes to kinetic store bc object is moving & thermal due to friction- temp increases)
force x distance is work done
1J=1Nm
one joule of work is done when force of 1N causes displacement of 1m
how do u use scale drawings to find resultant force
1- draw scale drawing of forces acting (first force to the end of last force)
2- draw resultant force from tail of first arrow to tip of last arrow
3- measure length of resultant with ruler,use scale to find N
4- use protractor to find bearing -clockwisefrom north, 3 digit
what is equilibrium
if all forces on object combine to give 0-object is in equilibrium
how can you split forces into components
split into 2 components at right angles to each other - horizontal and vertical- - overall has same effect as single force
or draw on scale grid and add components to grid lines, measure
how does stretching compressing or bending transfer energy
WORK IS DONE when a force is applied to an object it may stretch compress or bend (more than one force must be acting on object)
(elastic objects)it will be elastically deformed if it returns to original shape + length after force has been removed e.g. spring- energy goes to elastic potential energy store
inelastically deformed-doesnt return to original shape or length after force has been removed- ALL energy to elastic potential energy store
explain extension and spring constant
extension is directly proportional to force. the extension of a stretched spring to load/ force applied.
spring constant x extension = force
spring constant depends
explain extension and spring constant
extension is directly proportional to force. the extension of a stretched spring to load/ force applied.
spring constant x extension = force
spring constant depends on material you are stretching(stiffer spring= greater spring constant)
what is limit of proportionality
the limit to the amount of force you can apply to an objecy for the extension to keep on increasing proportionally
on graph - maximum force is shown where graph curves shows extension is no longer proportional to force
practical to investigate link between force and extension
1- measure natural length of spring when no load is applied, with mm ruler clamped to stand - take reading at eye level, - add a marker to bottom of spring to make reading accurate
2-add mass to spring, let it rest, record mass, measure new length of spring (extension is change in length)
3- repeat till you have no fewer than 6
4- plot force-extension graph- it will curve once limit of proportionality has been exceeded(non linear- spring stretches more for each unit increase in force)
(straight line in graph means force & extension is (gradient and spring constant) directly proportional)
how to calculate elastic potential energy
0.5 x spring constant x extension
what is a moment, how is it calculated
a force/forces cause object to rotate, turning effect of a force is called its moment
moment of force= force x distance
force on spanner causes moment
larger force/distance= larger moment
distance, d, is the perpendicular distance from the pivot to the line
of action of the force, in metres, m.
If object is balanced, total clockwise moment about a pivot= total anticlockwise moment about that pivot.
maxiumum moment= push at right angles (perpendicular) to spanner- other angles mean smaller distnace
function of levers
increase distance from pivot where force is applied. = less force is needed to get the same moment
makes it easier to do work(lift load or turn nut)
function of gears
transmit rotational effects of force from a place to another
circular disks with teeth around edges - teeth interlock so turning gear causes another to turn in opposite direction.
different sized gears used to change moment of a force
e.g. force transmitted to larger gear = bigger moment= bigger distance to pivot
larger gear turns slower than smaller gear
what is pressure in a fluid
presure is force per unit area= (PASCALS )particles exert pressure
pressure in fluids causes a force normal (at right angles) to any
surface in contact with fluid
pressure = force normal to a surface/
area of that surface
How can The pressure due to a column of liquid can be calculated
pressure = height of the column × density of the liquid
× gravitational field strength
(density in a liquid is uniform - doesnt vary) density in gas can vary
+ dense=+ particles=+ weight of particles = +pressure = LIQUID PRESSURE INCREASES WIH DEPTH
why do objects in fluids experience upthrust
object is submerged in fluid=pressure of fluid exerts force on it from all directions
pressure increases with depth- force exerted on bottom of object is larger than force acting at top of object (= resultant force= upthrust)
upthrust= weight of fluid that is displaced by object
explain how floating and sinking works
floating: if upthrust on object= objects weight- forces are balanced, object floats
sinking;if object is denser than the fluid , unable to displace enough fluid equal to its weight(weight is larger than upthrust)
(depends on density )
how do submaries make use of upthrust
to sink - large tanks filled with water to increase weight of submarine so it is more than the upthrust
to rise-tanks filled with compressed air to reduce weight so its less than upthrust
explain how atmospheric pressure works
atmosphere is layer of air around earth. pressure is made by air molecules colliding with earth’s surface
as altitude increases , atmosphere gets less dense due to less air molecules colliding with surface
there are fewer air molecules above surface as height increases so weight of air above it decreases with altitude
explain difference between distance and displacement
Distance is how far an object moves.(does not involve direction.)Distance is a scalar quantity.
Displacement includes both the distance an object moves(measured in a straight line from the start point to the finish point) and the direction of that straight line. Displacement is a vector quantity
explain difference between speed and velocity
how do you calculate speed
speed=scalar, velocity=vector
speed is how fast youre going but velocity is the speed in a given direction
constant speed with changing velocity= speed is same but direction is changing e.g. car on roundabout
speed= distance x time
typical speeds for everyday objects
person walking- 1.5m/s
running-3m/s
cycling-6m/s
car-25m/s
train-55m/s
plane-250m/s
sound-330m/s
how does the speed of different factors vary
speed of person running,walking,cycling varies on age, distance, fitness travelled
speed of sound depends on what the sound waves are travelling through
speed of wind varies with temperature and atmospheric pressure(& if there is buildings by e.g. forests reduce the speed of air)
what is acceleration how is it calculated
acceleration is the change in velocity in a certain amount of time
change in velocity/time
how to estimate accelerations
1- give a sensible speed for the object/vehicle
2-estimate how long it would take to stop
3-(change in velocity)/ time
if it is decelration place a minus sign
what is uniform acceleration
also known as constant acceleration
-acceleration due to gravity is uniform = 9.8m/s^2 near earth, same gfs
final velocity^2 - initial velocity^2 = (2 x acceleration x distance)
