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physics > 5 - forces > Flashcards

5 - forces Flashcards

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1
Q

whats vector and examples

A

magnitude and direction
- force/velocity/displacement/accelaration/momentum etc…

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2
Q

whats scalar and examples

A

only has magnitude (no direction)
- speed/distance/mass/temp/time etc….

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3
Q

whats a contact force and examples

A

2 objects need to be touching for a force to act
- friction/air resistance/ normal contact force

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4
Q

whats a NON contact force and examples

A

objects don’t need to be touching for a force to act
- magnetic/electrostatic/gravitational

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5
Q

effects of gravity

A
  • gives everything a weight
  • makes everything fall to the ground on earth
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6
Q

whats mass

A
  • the amount of stuff inside an object
  • the same anywhere in the universe
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7
Q

what is weight

A
  • the force acting on an object due to gravity
  • depends on the gravitational field strength so varies in different locations
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8
Q

how to calculate the resultant force on a free body diagram

A
  • horizontal and vertical
  • large value - smaller value
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9
Q

whats work done

A

the amount of force needed to move an object a certain distance

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10
Q

when is an object in equillibrium

A

if all the forces acting upon it give a resultant force of 0

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11
Q

elastically deformed and inelastically deformed

A
  1. can return to original shape and length after the force has been removed
  2. cant return back to its original shape and length after the force has been removed
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12
Q

what is the moment and how do you get a larger one

A
  • the rotational or turning effect of a force
  • eg spanner turning around a nut (pivot)
  • larger force and longer distance from pivot would mean a larger moment
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13
Q

whats a lever

A
  • increases the distance from the pivot at which the force is applied - less force for the same moment
  • basically they make it easier to do work eg like a load or turn a nut
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14
Q

what are gears

A
  • circular discs with ‘teeth’ around the edges
  • their teeth interlock so turning one turns another in the opposite direction
  • large gear = bigger moment bc distance from pivot is larger
  • larger gear will turn slower than smaller gear
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15
Q

what’s the pressure of a fluid

A

a force is exerted at right angles to any surface in contact with this fluid

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16
Q

whats the effect of depth of the pressure of a liquid

A

the pressure increases bc the number of particles above that point increases

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17
Q

whats upthrust

A
  • a force that pushes upwards on an object submerged in a fluid
  • equal to the weight of the fluid that has been displaced by the object
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18
Q

effect of weight of an object and upthrust

A

if weight is more than the upthrust the object skins
if the weight is less than the upthrust the object floats

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19
Q

how do submarines sink and float

A
  • SINK - large tanks are filled w water to increase weight so sub is more than upthrust
  • FLOAT - tanks filled w compressed air to reduce weight so sub is less than upthrust
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20
Q

whats the relationship between atmospheric pressure and height

A

the altitude (height above earth) increases as the atmospheric pressure decreases

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21
Q

distance and displacement

A
  • scalar - how far an objects moved
  • vector - distance and direction from starting point to finishing point
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22
Q

speed and velocity

A
  • scalar - how fast you are going
  • vector - how fast you are going at what direction
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23
Q

whats happening when objects move in a circle

A

constant speed but changing velocity (changing direction but at the same pace)

24
Q

every day speeds of walking/running/cycling/car/train/plane

A

walking - 1.5 m/s
running - 3 m/s
cycling - 6 m/s
car - 25 m/s
train - 55 m/s
plane - 250 m/s

25
Q

whats wind speed effected by

A
  • temp
  • pressure
  • obstacles - large buildings
26
Q

whats human speed effected by

A
  • old age
  • fitness
  • distance travelled
  • terrain
27
Q

whats acceleration

A

the change in velocity in a certain amount of time (how quickly you are speeding up)

28
Q

whats deceleration

A

the negative of acceleration (if something slows down the change in velocity is negative)

29
Q

distance time graph

A
  1. gradient = speed (steeper the faster)
  2. flat = stationary (its stopped)
  3. curves in gradient = acceleration/ deceleration
  4. straight line gradient = steady speed
30
Q

if an object is changing speed on a DISTANCE time graph - how can you find its speed at a specific point

A

draw a tangent to the curve at that point

31
Q

velocity time graphs

A
  1. gradient = acceleration
  2. flat = steady speed
  3. curves in gradient = changing acceleration
32
Q

how do you find the distance travelled from a VELOCITY time graph

A

find the area under that section

33
Q

whats friction

A

the force that acts in the opposite direction to movement

34
Q

whats drag

A

resistance you get in a fluid - eg air resistance is a type of drag

35
Q

how do you reduce drag

A

keep objects streamlined

36
Q

how does an object reach terminal velocity

A
  • when objects start to fall - force of gravity is more than the frictional force slowing it down - it accelerates
  • as the speed increases friction builds up
  • this gradually reduces acceleration until frictional force is equal to the accelerating force
37
Q

what is terminal velocity

A
  • resultant force of 0
  • fall at a steady speed
  • falling object —> frictional force is equal to the accelerating force
38
Q

newtons first law

A

“if the resultant force of a stationary object is 0, the object will stay stationary. if the resultant force on a moving object is 0 it will carry on moving at the same velocity” ——> resultant force is needed to make something start moving/speed up/slow down etc

39
Q

newtons second law

A
  • force and acceleration are directly proportional
  • the larger the resultant force acting on an object, the more the object accelerates
  • acceleration and mass are inversely proportional
  • object with a larger mass will accelerate less
  • F = ma
40
Q

whats inertia

A

when objects move at a steady speed they stay moving at a steady speed - this tendency to continue in the SAME STATE OF MOTION is called inertia

41
Q

what does inertia mass tell you

A

how difficult it is to change the velocity of an object

42
Q

newtons third law

A
  • “when 2 objects interact, the forces the exert on each other are equal and opposite”
43
Q

example of man pushing on wall - newtons third law in EQUILIBRIUM

A
  • man pushes wall
  • normal contact force acts back on him
  • these forces are the same size
  • as man pushes the wall the wall pushes back with an equal force
44
Q

different between newtons third law and newtons third law in eq

A
  • normal 3rd law –> exerting equal and opposite but if one has a smaller mass it will accelerate away further
  • eq - northing ever moves bc forces are equal
45
Q

equation for stopping distance

A

thinking distance + breaking distance

46
Q

what is thinking distance

A

how far the car travels during the drivers reaction time

47
Q

what is braking distance

A

distance taken to stop under the breaking force

48
Q

factors that effect thinking distance

A
  • speed your going at - the further u will travel during ur thinking time
  • reaction time - the longer ur reaction time the longer your thinking distance
49
Q

factors that effect braking distance

A
  • speed - the faster the car moving the longer it will take to stop
  • weather/road surface - wet or icy - skids
  • condition of tyres - bald tired cant get rid of water in wet conditions - skidding
  • condition of brakes - worn/faulty - wont be able to apply as much force
50
Q

what happens when you push the brake pedal of a car

A
  • push the brake pedal which causes the brake pads to press onto the wheels
  • this contact causes friction which causes work to be done
  • this work done btwn brakes and wheels transfers energy from kinetic energy stores of the wheels to the thermal energy stores of the brakes
  • the brakes increase in temperature
51
Q

how to measure reaction time

A

the ruler drop test - practical

52
Q

what is momentum

A
  • greater the mass of an object , the greater its velocity = it has more momentum
  • vector
  • mass x velocity
53
Q

conservation of momentum

A

in a closed system the total momentum before an event is equal to the total momentum after the event

54
Q

what safety features do cars have

A
  • crumple zones - crumple on impact increasing time taken for car to stop
  • stretchy seatbelt
  • air bags
55
Q

how do bike helmets protect us

A
  • crushable layer of foam - reduces impact on brain
56
Q

how do crash mats protect us

A
  • cushioned playground flooring - soft and compressible

physics (14 decks)

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