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Physics > P5 - Forces > Flashcards

P5 - Forces Flashcards

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1
Q

What are vector quantities

A

Have a magnitude and direction

E.g velocity p, acceleration , force, momentum, displacement

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2
Q

What’s a scalar quantity

A

Magnitude and no direction

Speed, distance, mass, temperature and time.

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3
Q

What are vectors shown with

A

An arrow. Length = magnitude and direction = direction.

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4
Q

What’s a contact force

A

Two objects touching for a force to act. Force, air resistance

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5
Q

What’s a non contact force

A

Objects don’t need to touch for the force to act

Magnetic, gravitational, electrostatic

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6
Q

What’s an interaction pair

A

Pair of forces that are equal and opposite and act on two interacting objects e.g chair exerts a force on the ground, ground pushes back with the same force. Equal but opposite and felt by both

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7
Q

What is gravitational force

A

The force of attraction between masses. Gravity attracts all masses but only noticeable when mass is very big

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8
Q

What effects does gravitational forces have

A

On surface of planets, it makes all things fall towards the ground
Gives everything a weight

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9
Q

What is mass

A

The amount of stuff on an object. The same everywhere in the universe

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10
Q

What is weight

A

Force acting on object due to gravity (pull of gravitational force on object)

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11
Q

Gravitational forces varies with…. and why

A

Varies with location. The closer you are to the mass causing the field the stronger it is. Larger mass = stronger

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12
Q

Mass and weight are

A

Directly proportional
Increase mass = increase weight
Double mass = double weight

Weight = mass x gravitational field strength

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13
Q

What are free body diagrams

A

Diagrams that describe all forces acting on an isolated object or system

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14
Q

What is resultant force

A

Overall force on a point or system

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15
Q

What can you replace a number of forces acting at a single point with

A

Replace with a single force (as long as the single force has the same effect as the other forces) - resultant force

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16
Q

How to find overall effect of all forces acting on same lines

A

Adding those in the same direction and subtracting those in the opposite

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17
Q

What happens if the resultant force moves an object

A

Work is done

When a force moves an object through a distance, work is done/energy is transferred to the object

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18
Q

To make something move you need…

A

A force to be applied, and a source of energy(food/fuel)

Force does work to move the object and energy is transferred

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19
Q

One joule of work is done when

A

One newton causes an object to move a distance of 1 metre

1 joule = 1 newton metre

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20
Q

How to use scale drawings

A

Draw all forces on an object to scale
Straight line from start of first force to end of last force
This is the resultant force, measure to find magnitude and angle for direction

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21
Q

What is equilibrium

A

Object is in an equilibrium if the forces on it are balanced
If all forces on an object give resultant force = 0, the object is in equilibrium
On scale diagram, this means the tip of the last force you drew will end where your first force began

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22
Q

Key information on split forces into components

A

Some forces act at awkward angles
Split into two components at right angles
Acting together, these components have the same effect as the single force

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23
Q

What happens when you stretch, compress or bend something

A

You apply a force, need more than one force acting (otherwise it would go in the same direction rather than change shape)

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24
Q

What does elastically deformed mean

A

Object that can go back to its original shape and length after force removed

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25
Q

What’s inelastically deformed

A

If object doesn’t return to original shape and length after force removed

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26
Q

When is work done with stretching

A

Work is done when force stretches or compresses an object and causes energy to be transferred to the elastic potential energy store. If it’s elastically deformed, all energy transferred to the EPES

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27
Q

Extension is

A

Directly proportional to force

Force = spring constant x extension x spring constant
Also works for compression

28
Q

There’s a limit to amount of force you can

A

Apply to an object to keep it increasing proportionally

29
Q

What is displacement

A

Measures distance and direction of a straight line

30
Q

What is velocity

A

Speed at a given direction

31
Q

Object moving in a circle at a constant speed has a….

A

Constantly changing velocity

32
Q

Typical everyday speeds…. running walking cycling car train plane

A 
Walking 1.5 m/s
Running 3m/s
Cycling 6m/s
Car 25m/s
Train 30m/s
Plane 250m/s
Speed of sound in air 330m/s changes depend on what sound waves are travelling through
33
Q

What is wind speed affected by

A

Temperature, atmospheric pressure, large buildings near by

34
Q

What is acceleration

A

How quickly you’re speeding up. It’d also the change in velocity over a certain amount of time

Acceleration = change in velocity/time

35
Q

What is uniform acceleration

A

Constant acceleration. Like acceleration due to gravity is uniform in free fall.

Final velocity^2 -initial velocity^2 = 2acceleration x distance

36
Q

Key information on distance time graph

A 
Gradient = speed (speed = distance/time)
Flat = stationary 
Straight uphill = steady speed 
Curves = acceleration or deceleration
Find speed at a point by drawing tangent and finding gradient
37
Q

Key information of velocity time graphs

A

Gradient = acceleration
Flat = travelling at steady speed
Stepper = greater acceleration or deceleration
Curve = changing acceleration
Area under graph = distance travelled.
Use tangent gradient to find acceleration at point

38
Q

What will happen if an object has no force propelling it

A

It will always slow down and stop due to friction

39
Q

Friction acts in…

A

The opposite direction to movement

40
Q

What is friction through a liquid called

A

Drag

41
Q

Drag increases as

A

Speed increases

42
Q

Examples of drag (resistance in fluid or gas)

A

Air resistance

43
Q

How to reduce drag

A

Object into streamlined shape

44
Q

Objects falling through fluids reach a

A

Terminal velocity

45
Q

What happens when an object falls through air

A

As it starts, gravity is bigger than friction so the object accelerates. As the speed increases, so does drag and gradually reduces the acceleration until friction and acceleration are balanced. This is a terminal velocity

46
Q

Terminal velocity depends on what, and why

A

Depends on shape and area.
Less streamlined = lower terminal velocity
Objects with larger surface area = lower terminal velocity

E.g marble has a higher terminal velocity than a beach ball. More air resistance on beach ball so beach ball spends less time accelerating so it doesn’t speed up as much - this happens as the air resistance is large enough to quickly equal the accelerating force as the accelerating force is low

47
Q

Newton’s first law

A

A resultant force is needed to make something start moving, speed up or slow down

If the resultant force of a stationary object is 0, it won’t move.
If the resultant force on a moving object is 0, it’ll travel at the same velocity

48
Q

Acceleration is proportional to

A

The resultant force.

Larger resultant force on object, the more the object accelerates.

49
Q

Acceleration is inversely proportional to

A

Mass.

Larger mass = less acceleration

Resultant force = mass x acceleration

50
Q

What is inertia

A

The tendency for motion to remain unchanged

51
Q

Until acted upon by a resultant force, objects will…

A

Stay at rest or move at a constantly velocity if already moving

52
Q

What does an objects inertial mass measure

A

How difficult it is to change the velocity of an object

Mass = force/acceleration

53
Q

What is Newton’s third law

A

Equal and opposite forces act on interacting objects

When two forces interact, the forces they exert on each other are equal

54
Q

If you push something like a shopping trolley what will happen

A

The trolley will push back against you just as hard. If you stop pushing, so does the trolley -> works as the two forces acting on different objects

55
Q

Newton’s third law is an

A

Equilibrium
E.g man pushing against a wall. He pushes against it and there’s a normal contact force acting on him. These forces are the same size

56
Q

What is momentum

A

How much ‘oomph’ an object has (a property moving objects have)
Greater mass/velocity = greater momentum

Momentum = mass x velocity

57
Q

Momentum before =

A

Momentum after

Conservation of momentum

58
Q

What’s an emergency stop

A

Maximum force applied by brakes to stop in shorted possible distance.
Longer it takes for an emergency stop = higher risk of crashing

59
Q

Stopping distance =

A

Thinking distance + braking distance

60
Q

What is the thinking distance affected by

A

Speed - if it’s faster you’ll travel further in time

Reaction time - longer reaction = more distance

61
Q

What is the braking distance affected by

A

Speed - going faster = longer to stop
Weather or road surface - wet, icy, leaves = less grip
Tyre condition - bald tyres can’t rid of water = skidding
Quality of brakes - worn or faulty can’t apply as much force

62
Q

What does braking rely on

A

Relies on friction between the brakes and wheels

63
Q

How does braking a car work

A

Brake pedal pushes, which causes the brake pad to be pressed onto wheels which causes friction which causes work done. Work done transfers energy from the kinetic energy stores of wheels to thermal energy stores of brakes.
Brakes increase in temperature
Faster vehicle = more energy to KES = more work to be done
Larger braking force = larger deceleration
Large deceleration are dangerous as they cause brakes to overheat and skidding

64
Q

Typical reaction times

A

Between 0.2 and 0.9 seconds

65
Q

What are reaction times affected by

A

Tiredness, drugs, alcohol or distractions

Physics (7 decks)

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