Topic 5 Forces COPY Flashcards
Forces are either ——- or ——–
contact , noncontact
Force is ——– quantity
vector quantities have a magnitude and a direction
Some physical quantities have only ———- and no ————–
these are called ——————– quantities
magnitude and no direction
scalar
Examples of vector quantities:
force,velocity,displacement,acceleration,momentum etc
Examples of scalar quantities:
speed,distance,mass,temp,time etc
Vectors are usually represented by an arrow the length of the arrow shows the———and the direction of the arrow shows the ————-
magnitude
direction of the quantity
A force is
a push or pull on an object that is caused by it interacting with something
give an example of a contact force
friction, air resistance, tension in ropes
give an example of a non contact force
magnetism. gravitational force , electrostatic force
An interaction pair is a
pair of forces that are equal and opposite and act on two interacting objects
mass is just the amount of ———- for any given object this will have the —— value ———
‘stuff’ in an object.
same
anywhere in the universe
Weight is the ——
force acting on an object due to gravity
Gravitational field strength varies with location and its ——- the closer you are to the mass causing the field and stronger for larger——–
stronger
masses
weight is measured using a
newton-meter
Mass is not a ———-
and is measured in ———
force
kilograms
How do calculate an object’s weight if you can’t measure it equation
weight (N)= Mass (kg) * Gravitional Field Strength (N/kg)
Describe the forces acting on a skydiver and what these do
weight acts on him pulling him towards the ground and drag (air resistance) also acts on him, in the opposite direction
Step by step of how you work out resultant forces using scale diagrams:
1.Draw all forces on an object to scale ‘tip-to tail’
2. Then draw a straight line from the start of the first force to the end of the last force-this is the resultant force (in a triangle)
3. Measure the length of the resultant force on the diagram to find the magnitude and the angle to find the direction of the force (the bearing)
If all forces acting on an object combine to give a resultant force of 0, the object is in———
On a scale diagram this means that the —- of the last force you draw should end where the —- of the first force you drew begins.
E.g. for three forces, the scale diagram will form a——–
equilibrium.
tip
tail
triangle
You might be given forces acting on an object and told to find a missing force given that the object is in equilibrium to do this:
draw out the forces you do know (to scale tiptotail) join the end of the last force to the start of the first. this line is the missing force so you can measure its size and direction
makesure you know how to do top to tail diagrams
You can spilt a force into components because not all forces act ———- or ———– some exact as ——– angles
To make these easier to deal with they can be split into ————————————————
You can resolve a force (split it into components) by drawing it on a -scale grid-
horizontally vertically
awkward
two components at right angles to each other (usually horizontally or vertically)
when an object stretches compresses or bends you need ———————- force otherwise the object would simply ——- in the direction of the ———– instead of ———————
more than one
move
applied force
changing shape
An object has been elastically deformed if it can go back to its’s …….:
original shape and length after the force has been removed
If an object has been in-elastically deformed if it :
doesn’t return to it’s original shape and length after the force has been removed
elastic objects are only elastic ———
up to a certain point
The extension of a stretched spring isdirectly proportional to
So the equation is
This equation also works for com—–where e is
directly proportional to the load or force applied
Force (N)= Ke
Spring Constant (N/m) * Extension (m)
compression
just the difference between the natural and compressed lengths- the compression
the spring constant k, depends on the material that you are stretching- a stiff spring has a ———— spring constant
greater
There is a limit to the amount of ——- you can apply to an object for the ———- to keep on increasing ——– this is known as the limit of ———
force
extension
proportionally
proportionality
extension is not just the —— of the spring its the———-between the stretched length and the ———– un-stretched length
length
difference
original
As long as a spring is not ———– past its limit of ————– work done in stretching or compressing a spring can be found using:
stretched
proportionality
E (J)= 1/2Kesquared
Spring constant (N/m) and extension in (m)
a moment is the
turning effect of a force
moment equation
what is the distance measuring?
moment (Nm)= Force (N)*Distance (m)
The perpendicular distance from the pivot to the line of action of the force
if the total anticlockwise moment equals the total clockwise moment the object is :
balanced and won’t turn
moments help you to get the most out of a ——- force and transmit forces across ——————-
most
across a distance
Levers increase the ——– from the pivot at which the ———- is applied and since moment = force*distance this means that less ——- is needed to get the ——- moment
distance
force
same
moment
Gears are———- with ———– around their ———-
Their ‘——-‘ ——– so that turning causes ———- to turn in the ——————–
They are used to ———- the ——— effect of a ————- from one ——– to ———-
circular discs
‘teeth’ around their edges
teeth interlock
another
opposite direction
transmit
rotational
force
place
another
Why are different size gears used?
A force transmitted to a larger gear will cause a ——— because …..
The larger gear will turn ——– than the smaller gear
to change the moment of a force
bigger moment
the distance to the pivot is greater
slower
Fluids are substances that can —-because their particles are able to —– around
As these particles move around they collide with ———- and other ——– and exert a ——-
Pressure is force per —————so this means particles exert a ——–
‘flow’ move
surfaces
other particles
force
unit area
pressure
The pressure of a fluid means a force is exerted normal (a right angles):
to any surface in contact with the fluid
You can calculate the pressure at the ——– of a fluid by using:
surface
pressure in pascals= Force (N)/Area of that surface (m/s quared)
Density is a measure of the ‘———-‘ of a substance how ——– together the particles in a ———– are
For a given liquid the density is ——–
The density of a gas can ——— though
compactness
close
substance
uniform
vary
The more dense a given liquid is the more —–it has in a certain space. This means this means there are more particles able to ———- so ——– is higher
particles
collide
pressure
As the depth increases the number of particles —— that point ———. The ——- of these particles adds to the ——– felt at that point . So liquid ——— increases with depth.
above increases
weight pressure
pressure
upthrust determines whether an object will —- or ——
sink , float
when an object is submerged in a fluid (either partially or completely) the——– of the fluid exerts a ——-on it from ————-
———–increases with depth so the force exerted on the bottom of the object is ——–than the force acting on top of the of the object
This causes a ——- force upwards known as ——–
The upthrust is equal to the weight of the —— that has been ——– by the object.
pressure
force
every direction
Pressure
larger
resultant
upthrust
fluid
displaced
If the upthrust on an object is equal to the objects weight then:
If an objects weight is more than the upthrust :
This means that whether or not an object will ——- depends on its ————
the forces balance and teh object floats
it sinks
float
density
How do submarines make use of upthrust?
To sink large tanks are filled with water to increase the weight of the submarines so that it is more than the upthrust . To rise to the surface, the tanks are filled with compressed air to reduce the weight so that its less than the upthrust
Atmospheric pressure is :
It’s acting on you at….
and varies with your height …
it is created on a surface by:
The atmosphere is a layer of —— that surrounds the ——
the pressure exerted by the air around you.
all times
above sea-level
air molecules colliding with the surface
air , earth
atmospheric pressure ———- with height
This is because:
decreases
as the altitude increases the atmosphere gets less dense so there a fewer air molecules that are able to collide with the surface. There are also fewer air molecules above a surface as the height increase. This means that the weight of the air above it, which contributes to atmospheric pressure, decreases with altitude
Why do mountain climbers carry gas tanks:
lower density of air higher up so less air particles so less oxygen
Distance is a ———- quantity because it doesn’t involve ———
Displacement is a ———- quantity
scalar
direction
vector
speed an velocity both measure how fast you are going but speed is ——— and velocity is a ——–
scalar
vector
average speeds for:
a person walking speed
a person running speed
a person cycling speed
a car speed
a train speed
a plane speed
1.5 m/s
3 m/s
6 m/s
25 m/s
55 m/s
250 m/s
the speed of sound at —— in air changes depending on what the sound waves are travelling through
330 m/s
wind speed can be affected by things like;
temp, large buildings an atmospheric pressure
acceleration is
the rate of change of velocity
for cases of constant acceleration you can use the equation:
acceleration (m/s squared)= change in velocity (m/s)/ time in seconds
uniform acceleration means a ——–
acceleration due to gravity is ——- for objects in free fall . It’s roughly ——- near the earth’s surface and has the same value as ————————
you can use this equation for uniform acceleration:
constant acceleration
free fall
9.8 m/s squared
gravitational field strength
(final velocity in m/s) squared - ( initial velocity m/s) squared= 2acceleration(m/squared)distance(m)
If an object has no force propelling it along it will always —————— and ———- due to ———–(unless you’re in space an theres nothing to rub against)
———- always acts in the ——– direction to movement
slow down and stop
friction
friction
opposite
To travel at a ——- speed the driving force needs to ———— the frictional forces
You get friction between two surfaces in ——— or when a object passes through a ———- this is called ———
air resistance is a type of ———
The most important by far in reducing ——— is keeping the object ———-. This is where the object is ——– to allow fluid to ——— it reducing ———- parachutes work in the ——– way they want as much ——- as possible
steady
balance
contact
fluid
drag
drag
drag
streamlined
easily flow across
drag
opposite
drag
drag increases as —— increasess
speed
when talking about resistive forces in exam when object travelling through air say ‘air ———-‘ and not drag
resistance
If an object falls for long enough it will reach its ————- velocity / maximum ———
terminal
speed
How do objects falling through a fluid reach a terminal velocity:
1.when falling objects first set off the force of gravity is much more than the frictional force slowing them down so they accelerate
- as the speed increases the friction builds up
3.This gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force ( so the resultant force is zero)
- It will have reached its maximum speed or terminal velocity and will fall at a steady speed
terminal velocity depends on —— and ——–
The accelerating force acting on all falling objects is ————and it would make them all fall at the same ——-, if it wasn’t for ——–
shape
area
gravity
rate
air resistance
Newton’s first law say’s that
if the resultant force on a stationary object is 0 the object will remain stationary. If the resultant force on a moving object is 0it’ll just carry on moving at the same velocity (same speed and direction)
an non 0 resultant force will always produce acceleration or deceleration in the ———- of the force
direction
newtons second law :
that F (N)= m(kg)a (m/s squared), or resultant force is equal to mass times acceleration. A larger resultant force acting on an object causes a larger acceleration, and objects with larger mass require more force to accelerate.
Inertia is the ——– for motion to remain unchanged.
Until acted on by a—– objects at rest —– at rest and objects ——— stay at a steady speed will stay moving at that —– this tendency to continue in the same state of —– is called ——-
An objects’ inertia mass measures:
Inertia mass can be found using:
tendency
force
moving
speed
motion
inertia
how difficult it is to change the velocity of an object
Newtons second of law of motion f=ma rearranging this to m=f/a so inertia mass is just the ratio of force over acceleration
Newtons third law says that:
If you push something say a shopping trolley , the trolley will push back against you just as ——and as soon as you stop pushing so does the ——
The slightly tricking thing to get your head around is that if the forces are always—-how does anything go anywhere?
The important thing to remember is that the two forces are acting on ——— objects
when two objects interact the forces they exert on each other are equal and opposite
hard
trolley
equal
different
Stopping distance=
thinking distance + braking distance
the thinking distance :
how far the car travels during the driver’s reaction time
The braking distance:
the distance taken to stop under braking force
thinking distance is affected by:
your speed- the faster your going the further you’ll travel during the time you take to react
your reaction time- the longer your reaction time the longer your thinking distance this can be affected by tiredness drugs, or alcohol. distractions like kids in car can also affect your ability to react
Braking distance is affected by :
your speed- for a given braking force, the faster a vehicle travels, the longer it takes to stop
The weather or road surface - if it is wet or icy or there are leaves or oil on the road there is less grip ( less friction) between a vehicles tyres and the road which can cause tyres to skid
The condition of the tyres- if the tyres are bald- (they don’t have any thread left) then they cannot get rid of water in wet conditions . This leads to them skidding on top of the water.
How good your brakes are- if brakes are worn or faulty they won’t be able to apply as much force as well maintained brakes, which could be dangerous when you need to brake hard.
the longer your stopping distance the more ——– you need to leave —— of a car to stop ———
space
in front
safely
A typical reaction time is between —- and —- seconds
0.2 and 0.9
braking relies on ——-between the ——– and ———
when the brake pedal is pushed this causes:
This ——- causes ——– which causes ———
The ———— between the brakes and the wheels transfers energy from the ———- stores in the wheels to the ————— of the brakes . The brakes increases in ———-.
The faster a vehicle is going the more energy it has in it ——– store , so the more —— needs to be done to ——- it . This means that a greater —— force is needed to make it —— within a —————-
A larger braking force means a ————- deceleration . very large decelerations can be ——–because they may cause :
friction
brakes pedals
brake pads to be pressed onto the wheels .
contact
friction
work to be done
work done
kinetic energy stores
thermal energy stores
temp
kinetic energy
work
stop
braking
stop
certain distance
large
dangerous
brakes to overheat (so they don’t work as well) or could cause the vehicle to skid
speeds affects braking distance more than ——- distance
thinking
momentum equation
the greater the —- of an object or the greater its ———– the more momentum it has
It is a ———– quantity
momentum (kg m/s)= mass (kg) * velocity m/s
mass
velocity
vector
In a closed system which is just a fancy way of saying:
The total momentum before an event (eg.colision) is the —– after an event. This is called:
that no external forces act on something
same
conservation of momentum
A moving car hits into the back of a parked car. The crash causes the two cars to lock together and they continue moving in the ——– that the original moving car was travelling but at a —————
So before:
So after:
direction
lower velocity
The momentum = to mass of moving car * its velocity
The mass of the moving object has increased but its momentum before the collisionis equal to momentum before the collision so an increase in mass causes a decrease velocity
If the momentum before an event is 0 then the momentum after will be ——– After an explosion pieces fly off in different directions so that ——– cancels out to ——
0
total momentum
0
when a force acts on an object it causes it to ——————
The bigger the force the ————- the change in momentum
change momentum
faster
You know when a non zero resultant force acts on a moving object or object that can move it causes its ———— to change this means that there is a change in momentum
so f=
change in velocity/change in time
Force (N)= change in momentum in (kg m/s)/ change in time (s)
Conservation of momentum explains why a gun or cannon recoils backwardswhy :
when it is fired. When a cannon is fired, the cannon ball gains forward momentum and the cannon gains backward momentum. Before the cannon is fired (the`` ‘event’), the total momentum is zero. This is because neither objectThe total momentum of the cannon and the cannon ball after being fired is also zero, with the cannon and cannon ball moving in opposite directions.
crash mats and cushioned playground flooring increase the time taken for you to stop if you fall on them. this is because they are made from :
soft compressible (squish-able) materials
Explain why a car has a maximum speed
(6 marker)
there is a maximum forward force
as the speed of the car increases air resistance increases until air resistance is equal in size to forward force so the car can no longer accelerate
What about bike helmets why are they safe?
contain a crushable layer of foam which helps to lengthen time taken for your had to stop in a crash reducing impact on brain
Cars have many safety features such as and what they do:
crumple zones:
which crumple on impact, increasing the time taken for the car to stop
seat belts: which stretch tightly increasing time taken for the wearer to stop
Air bags inflate before you hit the dashboard of a car . the compressing air inside it slows you down more gradually than if you has just hit the hard dashboard.
