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My Physics > Section 1: Forces and Motion > Flashcards

Section 1: Forces and Motion Flashcards

1
Q

Scalar quantities

A

Scalars have a magnitude (size) only

e.g temp and speed

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2
Q

Moments definition

A

Moment = the turning effect of a force

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3
Q

Principal of moments

A

If the object is in equilibrium:

sum of clockwise moments = sum of anti-clockwise moments

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4
Q

Centre of mass

A

The point where the whole of the mass of the object appears to be concentrated

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5
Q

Vector quantities

A

Vectors have both magnitude and direction

e.g force and displacement

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6
Q

Resultant force

A

The sum of all forces acting

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7
Q

Reaction / contact force

A

Force created by a body as a a reaction to a force being applied

e.g a book on a table

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8
Q

Upthrust

A

Upward force on a body caused by the fluid (water or gas) being displaced around it

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9
Q

Gravitational force

A

Force due to gravitational attraction. Can act at a distance

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10
Q

Magnetic force

A

Force caused by magnetic attraction. Can act at a distance

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11
Q

Electrostatic force

A

Force caused by attraction between charges. Can act at a distance

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12
Q

Engine force

A

Forward force e.g created by a car engine

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13
Q

Tension

A

Force tending to stretch or elongate something

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14
Q

Lift

A

Upward force on a airplane

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15
Q

Friction

A

Resistant force that opposes the motion of an object

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16
Q

Air/water resistance / Drag

A

Frictional force caused by particles colliding with the body that opposes motion

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17
Q

Newton’s 1st law

A

An object will remain stationary or continue at a constant velocity, unless acted upon by a resultant force

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18
Q

Newton’s 2nd law

A

F = m x a

Force (N) = mass (kg) x acceleration (m/s2)

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19
Q

Newton’s 3rd law

A

For every action there is an equal and opposite reaction

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20
Q

Stopping distance

A

Stopping distance = Thinking + Braking distance

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21
Q

Factors affecting thinking distance

A
  • age
  • tiredness
  • influence of alcohol/ drugs
  • speed of car
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22
Q

What is thinking distance

A

Distance travelled between when the driver has seen the hazard and puts his foot on the brake

thinking distance = reaction time x speed

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23
Q

What is braking distance

A

Distance travelled when driver puts foot on brake and car stops

24
Q

Factors affecting braking distance

A

-condition of road (icy, slippery)
-tyres
-quality of brakes
-speed of car
(if speed doubles, braking distance is 4 times greater)

25
Q

Equation for average speed

A

Average speed = total distance / Time

m/s

26
Q

Equation for acceleration

A

acceleration = change in velocity / time taken for change

m/s2

27
Q

Equation for velocity

A

velocity = displacement / time

(m/s) + direction

28
Q

Velocity - time graphs

A

(see ipad)

-gradient is acceleration (rise/run)
-area under graph is distance travelled
Area = 1/2 x base x height

distance = 1/2 x a x t2
= 1/2 x acceleration x time2

29
Q

What is a force?

A

A push or pull

30
Q

Gradient of graphs

A

rise/run

y/x

31
Q

Displacement - time graphs

A

(see ipad)

  • positive velocity is moving away from point
  • negative velocity is moving towards point
32
Q

independent and dependent variables and their axis

A

independent variables : x axis

dependent variables : y axis

33
Q

Draw a v/t graph for a parachutist from jumping to landing

A

Check iPad

34
Q

Equation for moments

A

Moments = force x perpendicular distance from the pivot

35
Q

Equation relating weight, mass and gravity

A

Weight = mass x gravity

kg) (N) (10N/Kg

36
Q

Resultant force diagrams

A
  • Square or circle in the middle

- Find the difference between forces, use arrow to denote which direction the resultant force is acting

37
Q

Describe the forces acting on a parachutist from 0 - 40 seconds

A

When a parachutist jumps out a plane:

  1. 0-2 s: The parachutist accelerates very quickly towards he ground due to his weight being greater than drag. The resultant force and velocity is very large
  2. 0-8 s: The parachutist accelerates slower towards the ground due to increase in drag. The acceleration and resultant force is lower
  3. 10-15s: The weight and the drag balances out and the resultant force is zero. This means that the parachutist has reached terminal velocity and is no longer accelerating
  4. 15-17s: The parachutist opens his parachute and decelerates very quickly. The air resistance increase dramatically and the weight stays the same so the upward resultant force increases. The velocity decreases.
  5. 17-20s: The parachutist decelerates slower and as weight and drag balance out. The resultant force and velocity is smaller. The acceleration is slower.
  6. 21-39s: The weight and drag balances out again and the resultant force is zero. The parachutist reaches a new terminal velocity and is no longer accelerating.
38
Q

How to calculate weight?

A

w = mass x gravity

39
Q

what do distance-time graphs show?

A

speed

time on x axis
distance on y axis

gradient = velocity

40
Q

How is average speed calculated ?

A

total speed / total time

41
Q

Define a moment

A

a turning effect of a force

42
Q

How to calculate a moment

A

moments (N/m) = force(N) x perpendicular distance from a pivot (m)

43
Q

How does a an object’s weight act?

A

throughout the centre of mass

44
Q

What is the purpose of a counterweight of a crane

A
  • To prevent the crane from toppling over, concrete blocks are suspended at the other end of the load arm
  • Act to create a moment that opposes moment of load
45
Q

Describe an experiment to find the COM of an object

A
  1. Drill a hole and hang up the object
  2. Hang a plumb line from the suspension point
  3. Mark the vertical line
  4. Drill another hole in a different position and draw a line where the plumb line suspends. Repeat
  5. The point where the lines meet is the centre of mass
46
Q

Describe the changes in support on bridge as a vehicle moves from one side to the other

A
  • When the lorry is at the middle of the bridge its weight is equally supported by column A and B
  • When the lorry moves to column A then all upward force will be at column A
  • When the lorry is 1/4 of the way, the column nearest to him will support 3/4 of his weight
47
Q

Draw force diagrams of a vehicle on a bridge

A

Check on iPad

48
Q

what is Hooke’s law

A

The extension of an elastic object (e.g spring) is directly proportional to the force applied, provided the limit of proportionality is not exceeded

49
Q

Identify Hooke’s law graphically

A

A straight line until near the end where it starts to curve

50
Q

Equipment for investigating Hooke’s law

A
  • spring
  • meter ruler
  • clamps
  • retort stand
  • 10 g slotted masses
51
Q

Define elasticity

A

Ability to return to original size and shape after having been deformed

52
Q

How to get accurate data when investigating Hooke’s law?

A

Exclude anomalous results

53
Q

Describe the relationship of a load v extension graph that obeys Hooke’s law

A

Provided the elastic limit is not reached:

  • straight line graph passing through the origin
  • directly proportional relationship

After the elastic limit:

  • stretches more for each successive increase in force
  • shape is permanently changed
54
Q

Draw a diagram of apparatus used in the Hooke’s law experiment

A

check on iPad

55
Q

What error might occur during the Hooke’s law experiment?

A

Random error: reading not taken at eye level

Systematic error:
using ruler with zero error
spring not in good condition, passed elastic limit already

56
Q

Describe Hooke’s law experiment

A
  1. Set up apparatus
  2. Add 10g mass to the holder and record the spring length
  3. Add another 10g and record new spring length
  4. Take away previous spring from current to calculate the extension
  5. Repeat until 100g is reached

improve by: repeating several times with different springs
decrease increments by which weight is added, more precise
continue adding weight beyond 100g

57
Q

Describe experiments to investigate the motion of everyday objects such as toy cars or tennis balls

A
  1. Attach one end of ticker tape to a toy car
  2. The ticker tape is pulled through the machine as the car moves
  3. Cut up the tape in length representing equal time
    5 dots equal 0.1 seconds, if the tape is pulled quickly the dots are further apart, tape pulled slowly, dots closer together
  4. Make a speed time graph

note: most school ticker tapes make 50 dots per second

My Physics (12 decks)

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