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Physics paper 2 > P5: Forces > Flashcards

P5: Forces Flashcards

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1
Q

What is a contact force?

A

When objects are physically touching

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2
Q

What are 4 examples of contact forces?

A

-Normal reaction force
-Friction
-Air resistance
-Tension

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3
Q

What is a non-contact force?

A

When the force is not touching the object

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4
Q

What are 3 examples of non-contact forces?

A

-Magnetism
-Electrostatic force
-Gravity

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5
Q

What is scalar?

A

A quantity that only has magnitude

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6
Q

What is vector?

A

A quantity that has magnitude and direction

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7
Q

How can we find the resultant vector?

A

-By adding them
-If at right angles, make a triangle and use pythagoras

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8
Q

What are 5 examples of scalar quantities?

A

-Distance
-Speed
-Mass
-Energy
-Temperature

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9
Q

What are 5 examples of vector quantities?

A

-Displacement
-Velocity
-Acceleration
-Force
-Momentum

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10
Q

What does it mean if there is no resultant force on a vector?

A

There is no acceleration

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11
Q

What is weight?

A

The force that gravity pulls an object down with

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12
Q

What is the equation for weight (N)?

A

Weight (N) = mass (kg) x gravitational field strength, g (N/kg)
W=mg

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13
Q

What is the gravitational field strength on earth?

A

g = 9.8 N/kg

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14
Q

What is the gravitational field strength on the moon?

A

g = 1.6 N/kg

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15
Q

What does work done mean?

A

Energy transferred by a force

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16
Q

What happens to the force of you hold an object or lift at a constant speed?

A

You must be pushing upwards with a force that’s the same size as it’s weight

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17
Q

What is elastic deformation?

A

When an object returns to it’s original shape after being deformed

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18
Q

What is Hooke’s law?

A

Force and extension are directly proportional

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19
Q

What is the equation involving Dorcas, spring constant and extension?

A

Force (N) = spring constant (N/m) x extension (m)
F = ke

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20
Q

What does a force, extension graph look like?

A

Straight line through the origin: (directly) proportional relationship

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21
Q

What does the gradient on a force extension graph show?

A

Spring constant

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22
Q

What is the equation to find elastic potential energy?

A

R = 1/2 ke^2

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23
Q

What are the steps involved in the stretching a spring practical?

A

-Add masses into spring to change force (e.g. 100g = 1N)
-Measure extension with ruler at each weight, plot F against e
-Gradient of graph = spring constant
-Avoid systematic error by lining up 0cm with bottom of spring
-Avoid parallax error by getting on eye level when measuring

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24
Q

What is the equation to find the moment?

A

Moment (Nm) = Force (N) x distance from pivot (m)

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25
Q

What is the principle of moments?

A

When the sum of (total) clockwise moments = sun of anti-clockwise moments, a system is in equilibrium (it will not turn)

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26
Q

What creates pressure underwater?

A

The weight of the column of water above an object pushing down on it

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26
Q

How can gears be used to increase moments?

A

By driving a large gear with a smaller one (they work on ratios: double the diameter, double the moment or ‘torque’)

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27
Q

What is the equation for pressure underwater?

A

Pressure (Pa) = height (m) x density (kg/m^3) x g (N/kg)
P = hpg

28
Q

What creates pressure in gas?

A

Particles colliding with the walls of it’s container, exerting a force on them

29
Q

How do we increase pressure in a gas?

A

-Decrease volume
-Add more gas
-Increase temperature

30
Q

What happens to the atmosphere in higher altitudes?

A

The atmosphere becomes less dense, meaning there is lower pressure

31
Q

What is the equation for pressure?

A

Pressure (N/m^2) = Force (N) / Area (m^2)

32
Q

What does the gradient of a distance/displacement-time graph show you?

A

The speed/velocity

33
Q

What does the gradient of a speed/velocity-time graph show you?

A

The acceleration

34
Q

How do you work out speed or velocity?

A

Speed or velocity (m/s) = distance or displacement (m) / time (s)
v = d/t

35
Q

How do you work out acceleration?

A

Acceleration (m/s^2) = change in velocity (m/s) / time (s)
a = v/t

36
Q

What does the area under the graph give us?

A

The displacement

37
Q

What is the average walking speed?

A

1.5 m/s

38
Q

What is the average running speed?

A

3 m/s

39
Q

What is the average cycling speed?

A

6 m/s

40
Q

What is Newton’s 1st law?

A

If no resultant force acts on an object, it’s motion will be constant (velocity will not change)

41
Q

What is Newton’s 2nd law?

A

F = ma
Force (N) = mass (kg) x acceleration (m/s^2)

42
Q

What is Newton’s 3rd law?

A

For every action (force), there is an equal and opposite reaction (force) (this is NOT balanced forces)

43
Q

What is the acceleration practical?

A

-Accelerate trolley on track with slotted mass on string over pulley
-Use light/photogates to measure acceleration
-Change force by removing masses and placing on trolley (to keep the total mass the same)
-Plot F against a, gradient = total mass

44
Q

What is inertia?

A

The tendency for an object’s motion to stay constant if no F

45
Q

What is the stopping distance equal to?

A

Thinking distance + braking distance

46
Q

What are 5 things that the thinking distance can be affected by?

A

-Speed
-Distractions
-Alcohol
-Drugs
-Tiredness

47
Q

What are 3 things breaking distance can be affected by?

A

-Speed: if vx2, braking distance x4 as Ek = 1/2mv^2
-Condition of brakes, tyres & road
-Weather conditions

48
Q

What is the equation linking momentum, mass and velocity?

A

momentum (kgm/s) = mass (kg) x velocity (m/s
momentum = mv

49
Q

What happens to the total momentum in any collision?

A

It is always conserved

50
Q

What happens to the momentum when it rebounds?

A

m1u1 = m1v1 +m2v2

51
Q

What happens to the momentum when coupling?

A

m1u1 = mv

52
Q

What happens to the momentum when it recoils?

A

0 = m1v1 + m2v2

53
Q

What can force measure with regards to momentum?

A

The rate of change of momentum

54
Q

What is the equation for change in momentum?

A

F = ma = m🔺v/t = 🔺(mv)/t = change in momentum / time

55
Q

What happens to the force when the time over which momentum is lost or gained increases?

A

The force decreases

56
Q

What are 3 things that increase collision time?

A

-Seat belts
-Air bags
-Crumple zones
Momentum is lost over a longer time so the force is reduced

57
Q

What does s stand for in Newton’s equations of motion?

A

Displacement (m)

58
Q

What does u stand for in Newton’s equations of motion?

A

Initial velocity (m/s)

59
Q

What does v stand for in Newton’s equations of motion?

A

Final velocity (m/s)

60
Q

What does a stand for in Newton’s equations of motion?

A

Acceleration (m/s^2)

61
Q

What does t stand for in Newton’s equations of motion?

A

Time (s)

62
Q

What is the initial velocity (u) if starting at rest?

A

0m/s

63
Q

What is the final velocity (v) if stopping?

A

0m/s

64
Q

What is the acceleration (a) if the only force involved is gravity?

A

9.8m/s^2

65
Q

v =

A

u+at

66
Q

s = (with final velocity)

A

(u+v/2)t

67
Q

s = (with acceleration)

A

ut+1/2at^2

68
Q

v^2-u^2 =

A

2as

Physics paper 2 (4 decks)

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