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gcse phys > forces > Flashcards

forces Flashcards

1
Q

scalar meaning with examples

A

they have magnitude (size) but no direction

speed, distance, mass

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2
Q

vector meaning with examples

A

have magnitude (size) and direction, shown with arrow

force, displacement, weight

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3
Q

what is a force

A

a push or a pull caused by an interaction

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4
Q

examples of contact force

A

friction, air resistance, tension in rope

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5
Q

examples of non contact force

A

magnetic force, gravitational force, electrostatic force

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6
Q

how to calculate resultant force using scalar drawing/ vector diagram

A

creating a parallelogram using given measurements then drawing vector/resultant force

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7
Q

how to find horizontals and verticals from scalar drawings/vector diagrams

A

use grid paper to draw angle and force. draw horizontal and vertical.

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8
Q

how to know if something has been elastically deformed

A

returns to original shape when (more than one) forces removed

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9
Q

what is the relationship between the force pulling on a spring and hire fr the spring stretches, and where are the limits?

A

extension is directly proportional to force
at limit of proportionality,

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10
Q

how to investigate relationship of force and extension

A

• set up: weighted clamp stand with two clamps attached, one with meter ruler and one with spring, ensure top of spring is at 0m
• record unstretched length at eye level
• hang 1N mass and record new length
• repeat, ensure spring is at rest
• calculate extension (length - original)
• plot extension against weight graph

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11
Q

unit for moment

A

Nm

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12
Q

why does force have to be perpendicular to the pivot when caluclating moment?

A

distance will decrease

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13
Q

how do you balance an object on a pivot

A

make anticlockwise moment = clockwise moment

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14
Q

how do leavers make it easier to do work

A

they increase the distance from the pivot, so less force is needed. they are force multipliers

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15
Q

how do gears make it easier to do work

A

larger gears have a larger radius, meaning larger distance to pivot, meaning moment is greatrr

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16
Q

why do fluids create pressure

A

the particles can flow. they collide with walls of container at right angles, meaning they exert a force, and pressure is N/m^2

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17
Q

unit for pressure

A

pascal (Pa)

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18
Q

how does density and pressure change as you get higher in atmosphere

A

density decreases as there are less aur molecules above

pressure decreases as particles no longer collide with earth’s surface

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19
Q

how does pressure change in a container of water

A

as depth (and density) increases, there are more water particles above, meaning there is a greater weight acting downwards, so pressure increases

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20
Q

why dies upthrust occur

A

pressure increases with depth, so
when an object is submerged, the bottom of the object has a larger pressure than the top.
this means the force acting on the bottom is larger than the top, meaning there is a resultant force upwards, upthrust.

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21
Q

what happens for something to float

A

upthrust must equal weight of object

meaning upthrust is equal to weight of water displaced.
less dense object means less water has to be displaced in order for water displaced to equal weight of object

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22
Q

what are some typical daily speeds

A

walking 1.5m/s
running 3
cycling 6
car 25
train 50
plane 250
sounds 330

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23
Q

what is speed and velocity like when car drives in circle

A

speed is constant
velocity is constantly changing as direction changes

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24
Q

straight uphill line on distance time graph vs velocity time graph

A

DT: travelling at constant speed
VT: accelerating at constant speed

25
Q

flat line on distance time graph vs velocity time graph

A

DT: stationary
VT: travelling at constant speed

26
Q

curved line on distance time graph vs velocity time graph

A

DT: accelerating/decelerating
VT: increasing acceleration/deceleratio

27
Q

how to find distance travelled (displacement) on velocity time graph

A

find area under graph

if curved, count squares

28
Q

when should you use each type of acceleration equation

A

change in velocity/time
when an object accelerates

v^2 - u^s = 2as
(final - initial = 2 x accel x distance)
when an object accelerates at a constant/uniform rate

29
Q

what happens when an object falls through a fluid, as example of skydiver in air

A

• when skydiver falls, weight is only acting force, due to gravity.
resultant force and acceleration: down
• as they fall, fricton with air molecules, air resistance, acts upwards.
weight > air resistance
resultant force and acceleration: down
• increase in velocity means increase in air resistance, until
air resistance = weight
resultant force: none
this means velocity stays constant. this is called terminal velocity
• parachute opens. surface area has increased, meaning so has air resistance
air resistance > weight
resultant force: upwards, skydiver decelerates
• decrease in velocity means decrease in air resistance, until
air resistance = weight
resultant force: none
this means velocity stays constant. skydiver is at lower terminal velocity.

30
Q

factors that effect terminal velocity of an object

A

shape and area
larger objects have greater area for force of friction to act, with same amount of gravitational force as smaller object

31
Q

what is drag

A

resistance you get in a fluid
e.g air resistance, friction

32
Q

what is newtons first law of motion

A

if the resultant force acting on a stationary object is zero, it will remain stationary
if the resultant force acting on a moving object is zero, it will remain moving at the same velocity

also known as inertia

33
Q

what do forces look like when something moves at constant velocity

A

driving force = drag force

34
Q

what is newtons second law

A

acceleration of an object is:
• proportional to the resultant force
(larger force = larger acceleration)
• inversely proportional to the mass of the object
(larger mass = smaller acceleration)

35
Q

give speed, acceleration and force of family car going from road to motorway

A

15m/s to 30m/s
requires 2m/s^2 acceleration
require 2000N force

36
Q

what is inertial mass and how do you find it

A

measure of how difficult it is to change velocity of an object
larger inertial mass = larger force for given acceleration
it is the ratio of force / acceleration

37
Q

what is newtons third law

A

when two objects interact, the forces they exert on each other are equal and opposite

38
Q

give example of newtons third law of motion

A

man paddling in canoe
paddle pushes on water, water pushes back on paddle. the forces are equal in magnitude, but opposite in direction

39
Q

what does the velocity time graph look like for a skydiver

A
40
Q

investigating acceleration practical

A

• attach trolley of known mass to a string that loops over a pulley and place 100g mass on other end, which will provide the force. place a light gate halfway, connected to data logger
• place piece of card with gap in middle on the trolley. this will be detected by the light gate twice
• as mass will accelerate trolley, string, and masses, so the acceleration of the system is being investigated
• draw a starting line and place front wheels just before it
• release trolley
• record measurements from light gate through data logger
• repeat twice to get average acceleration of the whole system

41
Q

investigate the effect of mass on acceleration practical

A

keep force at end of string constant, but attach mass to trolley to increase the mass of the system
mass has increased, force stays the same

42
Q

how does changing the mass in the acceleration practical prove newtons 2nd law

A

mass of system has increased, force remains the same
F = ma
so acceleration should decrease as
a = F/m

43
Q

how to investigate effect of force on acceleration practical

A

• start with three masses on the trolley and record acceleration
• move one mass from trolley to end of string and record
• mass of the system still remains the same, as everything is attached, however force is changing
• repeat, adding 1 mass

44
Q

how does changing the force of the acceleration practical prove newtons second law

A

accelerating force is increasing, mass f system stays the same
F = ma
acceleration should increase

45
Q

what is stopping distance with formula

A

distance it takes to perform emergency stop after seeing obstruction
thinking distance + braking distance

46
Q

what is thinking distance and what is it affected by

A

distance travelled during reaction time
• speed
• reaction time - tiredness, drugs, alcohol, distractions

47
Q

what is braking distance and what is it affected by

A

distance travelled after braking force
• speed
• weather
• road surface
• tyre conditions
• brake conditions

48
Q

example of stopping distance

A

typical family car at 30mph:
thinking: 9m
braking: 14m

49
Q

how to measure someones reaction time

A

• A rests hand on fixed surface
• B holds ruler so 0 hangs between thumb and forefinger
• B drops without warning, A catches quick as possible
• record measurement on ruler
• longer measurement = longer reaction time. research table to find reaction time

50
Q

relationship between speed and thinking distance versus speed and braking distance and why

A

speed & thinking: linear
speed & braking: exponential because:
kinetic energy = 1/2mass x velocity^2
meaning if velocity doubles, kinetic energy quadruples

51
Q

why is it dangerous for a car to decelerate

A

brake presses against wheel -> friction -> thermal energy
high speed requires large braking force, overheating

52
Q

what is momentum measured in and what affects it

A

kg m/s
mass and velocity

53
Q

what is the momentum of a stationary object

A

no momentum

54
Q

what is conservation of momentum

A

in a closed system, momentum before an even = momentum after event

55
Q

in terms of momentum, what happens when a moving car hits a parked car

A

both move at same momentum as initial momentum of moving car.

momentum is conserved and mass has increased, meaning they move in same direction at lower velocity

56
Q

how can you use conservation of momentum to calculate velocity or mass

A

momentum before = momentum after
find total momentum
so do calculations on each side 🤷‍♀️ (practice questions)

57
Q

relationship between force and momentum

A

force increases velocity
larger force = larger change in momentum

58
Q

how to reduce danger of change in momentum when stopping in a car

A

• crumple zone
• seat belt
• air bag
• helmet
• crash mat
all makes change of momentum slower, meaning smaller force

gcse phys (6 decks)

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