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topic 5 - forces Flashcards

1
Q

what is the difference between vectors and scalars

A

vector quantities have magnitude and direction
scalar only have magnitude

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2
Q

give examples of vector and scalar quantities

A

vector- force, velocity, displacement, acceleration , momentum
scalar - speed , distance, mass , tamperature , time

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3
Q

what does the length of a vector arrow show

A

magnitude

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4
Q

what is a contact force and give some examples

A

when two objects have to be touching for the force to act
e.g. friction , air resistance, tension , normal contact force

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5
Q

what is a non contact force and give examples

A

when objects do not need to be touching for the force to act
e.g. magnetic force, gravitational force, electrostatic force

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6
Q

what is an interaction pair

A

a pair of forces that are equal and opposite and act on two interacting objects

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7
Q

what are the two important effects of gravity

A

on the surface of a planet, it makes all things fall towards the ground
it gives everything a weight .

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8
Q

how does gravitational field strength vary with location

A

it is stronger the closer you are to the mass causing the field and stronger for larger masses

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9
Q

what is the equation that links mass, weight and gravitational field strength

A

weight = mass x gravitational field strength

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10
Q

what is the relationship between weight and mass

A

weight and mass are directly proportional

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11
Q

what is a resultant force ?

A

A resultant force is a single force that describes all of the forces operating on a body.

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12
Q

what is the equation that links work done distance and force

A

work done(j) = force(N) x distance (m)

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13
Q

how many Nm is one joule

A

1

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14
Q

how do you use scale drawings to find resultant forces

A

draw all the forces acting on an object , to scale , tip to tail
then draw a straight line from the start of the first force to the end of the last force, - this is the resultant force
measure the length of the resultant force on the diagram to find the magnitude and the angle bearing to find the direction of the force

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15
Q

what does it mean if an object is in equilibrium

A

if all the forces acting on an object combine to give a resultant force of zero
on a scale diagram this means that the tip of the last force you draw should emd where the tail of the first force you drew begins.

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16
Q

what three things can applying a force to an object do

A

may cause it to bend stretch or compress

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17
Q

what are the two types of deformation

A

elastic - it can go back to its originall shape and length after the force has been removed
inelastic - doesnt return to its original shape and length after the force has been removed

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18
Q

what is the equation that links force extension and spring constant

A

force(n) = extension(m) x spring constant (n/m)

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19
Q

what is the relationship between force and extension

A

force is directly proportional to the extension

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20
Q

does a greater spring constant mean a stiffer oject or a strechier one

A

stiffer

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21
Q

describe a graph for force against extention

A

straight line untill it curves at the end
there is a maximum force above which the graph curves showing that extension is no longer proportional to force. this is known as the limit of proportionality
the straight part is elastic deformation
the curve is inelastic

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22
Q

describe a practical for investigating the link between force and extension in springs

A

set up apparatus

pilot experiment to check masses are a good size
1. use an identical spring to the one you will be testing, load it with masses one at a time untill you reach 5 , measure the extension each time
2. work out the increase in the extension of the spring for each of the masses
3. if any cause a bigger increase than the previous masses , you have gone past the limit of proportionality and need to usse smaller masses
.

actual test

  1. measure the natural length of the spring with a mm ruler clamped to the stand , take the reading at eye level
  2. add a mass to the spring and allow it to come to a rest. record the mass and measure the new length of the spring. the extension is the change in lenght
  3. repeat untill you have enough measurements, no fewer than 6
  4. plot a force by extension graph of results , it will only curve if you reach the limit of proportionality .
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23
Q

what is the area under a force - extension graph equal to

A

energy in the elastic potential energy store of a stretched spring

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24
Q

what is the equaion that links force , moment and distance

A

moment (Nm) = Force x distance (perpendicular distance)

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25
what is a moment
the turning effect of a force
26
how do you get the maximum moment
push at right angles, pushing at any other angle means smaller distance and so smaller moment
27
how do levers make it easier for us to do work
levers increase the distance from the pivot at which the force is applied. this means less force is needed to get the same moment .
28
describe how gears work
gears are circular disks with teeth around their edges their teeth interlock so that turning one causes another to turn , in the opposite direction tjey are used to transmit the rotational effect of a force from one placce to another . different sized gears can be used to change the moment of the fordce a force transmitted to a larger gear wil cause a bigger moment as the distance to the pivot is greater. the larger gear will turn slower than the smaller gear
29
what are fluids
liquid or gas
30
what does it mean when a force is exerted normal
at right angles
31
what is the equation that links area , force normal to a surface and pressure
pressure = force / area
32
describe the density in a liquid
it is uniform ( doesnt change shape or size , the same everywhere
33
how does a more dense liquid increase pressure
the more dense a liquid is , the more particles it has in a certain space, this means there are more particles that are able to collide to the pressure is higher.
34
how does the depth of a liquid increase the pressure.
as the depth of the liquid increasesm the number of particles above the point increases. the weigth of these particles adds to the pressure felt at that point so liquid pressure increases with depth
35
what is the equation that links pressure , height of column of liquid, gravitational field strength and density of a liquid
pressure (Pascals) = H eight x density x gravitational field strength
36
how and why do objects in water experience upthrust
pressure increases with depth so the force exerted on the bottom of the object is larger than the force acting on the top of the object. this causes a resultant force upwards known as upthrust . the upthrust is equal to the weight of fluid that has been displaced by the object.
37
why do some objects float and some sink
if the upthrust on an object is equal to its weight , the forces balance and the object floats. if an objects weight is more than the upthrust the object sinks.
38
how does atmospheric pressure change
as the altitude increases. atmospheric pressure decreases this is because as the altitude increases, the atmoshpere gets less dense so there are less air molecules that are able to collide with the surface. there are also fewer air molecules above a surface as the height increases. this means that the weight of the air above it which contributes to atmospheric pressure decreases with altitude
39
is distance a scalar or vector quantity
scalar
40
is displacement a scalar or vector quantity
vector
41
is speed a vector or a scalar quantity
scalar
42
is velocity a vector or a scalar quantity
vector
43
what is the equation that links speed distance and time
speed = distance/time
44
what is the issue with the speed = distance /time equation
objects rarely travel at a constant speed it gives the average speed
45
what is the typical speed for each of these objects person walking person running person cycling a car a train a plane
a person walking - 1.5 m/s a person running - 3 m/s a person cycling - 6 m/s a car - 25 m/s a train - 30m/s a plane - 250m/s
46
what can affect the speed at which a person walks,runs or cycles
fitness age distance travelled terrain
47
what is the speed of sound in air and how can it change
330 m/s changes depending on what it travels through
48
what affect wind speed
temperature atmospheric pressure structures
49
what is acceleration and deceleration
the change in velocity in a certain amount of time deceleration is negative acceleration - if something slows down .
50
what is the equation that links acceleration - change in velocity - time
acceleration m/s^2 = change in velocity m/s / time s
51
what is uniform acceleration
constant acceleration
52
acceleration due to gravity is _________ for object in free fall . it is roughly equal to _._ m/s^2
uniform 9.8
53
what is the equation for uniform acceleration
final velocity (m/s ) - initial velocity = 2 x (acceleration x distance )
54
what is the gradient equal to on a distance - time graphe
gradient = speed the steeper the graph the faster its going
55
what do the flat sections show on a distance - time graph
stationary
56
what do straight uphill sections on a distance - time graph mean
travelling at a steady speed
57
what do curves on a distance - time graph represent
acceleration or deceleration
58
how do you find the speed at a point on a distance time graph when the object is accelerating
draw a tangent to the curve at that point and find the gradient
59
what does gradient on a velocity - time graph mean
acceleration
60
what are the flat sections on a velocity time graph
travelling at a steady speed
61
what does the area under any section of a velocity time graph tell you
equal to the distance travelled in that time interval
62
when do you get friction and how does it act
you get friction between two surfaces in contact or when an object passes through a fluid always acts in the oposite direction to movement
63
what is drag
the resistance you get in a fluid (liquid or gas)
64
what is the most important factor in reducing drag
keeping the shape of the object streamlined,
65
why does a 70 mph engine have to work harder than a 30 mph engine
frictional forces increase with speed. a car has more friction to work agaisnt at 70mph than 30 mph . so the engine has to work harder to maintain a steady speed
66
explain why a ball falling from the top of a tall building reaches terminal velocity
when it first sets off, gravity is more than teh frictional force slowing it down so it accelerates . as the speed increases, the friction builds up . this gradually reduces the acceleration untill the frictional orce is equal to the accelerating force. it will hace reached its maximum spead or terminal velocity and fall at a constant speed.
67
what on earth causes things to fall at different speeds
air resistance
68
what is terminal velocity determined by on earth
its drag in comparison to its weight
69
what is newton's first law .
if the resultant force on a stationary object is zero , the object will remain stationary. If the resultant force on a moving object is zero , it'll just carry on moving at the same velocity. therefore a resultant force is neededto make something start moving , speed up or slow down . acceleration is directly proportional to resultant force acceleration is inversely proportional to the mass
70
what are the five different forms of acceleration
starting, stopping, speeding up ,slowng down ,changing direciton
71
what is the formula for newtons second law
F (resultant force) = acceleration x mass (kg)
72
what is inertia
The tendency of an object to continue in its state of rest, or in uniform motion unless acted upon by an external force.
73
what is inertial mass
inertial mass measures how difficult it is to change the velocity of an object
74
how can inertial mass be found
using newtons second law F = ma
75
what is newton's third law
when two objects interact , the forces they exert on eachother are equal and opposite. forces have to be the same type of force
76
describe a practical where you would test newtons secon law , f = ma
1. set up equipment get a toy car attached to a piece of string the string is looped around a pulley the end of the string is attached to a 100 g mass the weight of the mass will provide the force acting on the car we also need a timer 2. on the desk , draw chalk lines at equal intervals e.g. every 10 cm 3. hold the car at the starting point 4. record the time taken for the car to pass each distance marker 5. record the experiment on a phone to get more accurate results. 6. repeat several times but decrease the mass on the string each time. to investigate how varying the mass of an object , affects the acceleration produced by a constant force . 1. keep the force constant 2. attach a mass to the toy car 3. record the car as it accelerates along the bench 4. repeat, increasing mass attached to the car
77
how does newtons second law explan the results of the practical used to test the law
F = ma F= weight of the hanging masses M = mass of whole system a = acceleration of the system . by adding masses to the trolley , the mass of the whole system increases, but the force applied to the system stays the same. this should lead to a decrease in the acceleration of the trolley . by transferring masses to the hook, you are increasing the accelerating force without changing the mass of the whole system . so increasing the force should lead to an increase in the acceleration of the trolley .
78
how is the distance it takes to stop a car in an emergency found (stopping distance )
stopping distance = thinking distance + braking distance
79
what are typical car braking distances
14 m at 30 mph 55 m at 60 mph 75 m at 70 mph
80
what is thinking distance affected by
your speed - the daster you are going, the further you will travel during the time you take to react. your reaction time - the longer your reaction time, the longer your thinking distance
81
what is braking distance 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 in the road, their is less grip and so less friction between a vehicle's tyres and the road which can cause the tyres to skid . the condition of your tyres - if the tyres on the vehicle are bald , 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 the brakes are worn or faulty , they wont be able to apply as much force as well maintained brakes, which may be dangerous when you need to brake hard
82
describe fully how brakes work
when the brake pedal is pushed , this causes brake pads to be pressed onto the wheels. this causes friction which causes work to be done. this transfers energy from kinetic energy to thermal energy store of the brake. the brakes increase in temperature. rthe fater a vehicle is goinh, the more energy in its kinetic so more work needs to be done to stop it. this means a larger braking force is needed . this means a larger deceleration . very large deceleraions can be dangerous as they may cause brakes to overheat or the vehicle to skid
83
how quick is a typical reation time .
between 0.2 and 0.9 seconds
84
what can affect a persons reation time
tiredness drugs alcohol distractions
85
describe how you would carry out an experient to measure peoples reaction time
1. sit with your arm resting at the edge of a table . get someone else to hold a ruler so it hangs between your thumb and forefinger , lined up with 0 . 2.without giving warning, drop the ruler. close your thumb and finger to try catch it as soon as possible. 3. the measurement on the ruler at te point where it is caught is how far the ruler dropped in the time it takes you to react. 4. the longer the distance the longer reaction time. repeat and calculate mean use the same ruler each time and same person dropping it. introduce distractions
86
describe a graph for thinking distance
linear as it increases at the same rate as speed
87
describe a graph for braking distance against speed
increases faster the more you speed up work done to stop the car is equal to the energy of kinetic energy store in the car so as speed doubles, the kinetic energy increases 4 fold the braking distance then increases 4 fold (2^2)
88
describe a graph for stopping distance
a combination of thinking and braking distance .
89
is momentum a vetor or scalar quantity
vector
90
what is the equation for momentum
momentum kg m/s = mass x velocity
91
what is conservation of momentum
in a closed system , the total momentum before an event is equal to the momentum after an event
92
what is the equation that links force, momentum change and change in time
force = change in momentum / change in time
93
what are safety features of a car
crumple zones crumple on impact , increasing the time taken for the car to stop. seat belts stretch slightly, increasing the 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 had just hit the hard dashboard
94
how do bike helmets protect you
they contain a crushable layer of foam which helps to lengthen the time takem for your head to stop in a crash. this reduces the impact on your brain
95
how do crash mats protect you
they increase the time taken for you to stop if you fall on them . this is becausethey are made from soft compressible materials

Physics (8 decks)

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