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Physics > P2 - Forces > Flashcards

P2 - Forces Flashcards

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1
Q

Define a vector quantity and give examples of some

A

They have magnitude and direction

Examples: force, velocity, displacement, acceleration, momentum

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2
Q

Define scalar quantity and give examples of some

A

They have magnitude but no direction

Examples: speed, distance, mass, temperature, time

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3
Q

What are vectors usually represented as?

A

An arrow on a diagram

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4
Q

Define a contact force

A

When two objects have to be touching in order for a force to act.
Examples: friction, air resistance

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5
Q

Define non-contact force

A

When the objects do not need to be touching for the force to act
Examples: magnetic force, gravitational force, electrostatic force

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6
Q

What is an interaction pair?

A

A pair of forces that are equal and opposite and act on two interacting objects (Newton’s Third Law)

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7
Q

What is the difference between weight, mass and gravity?

A 
Gravity = the force of attraction between masses (gives everything a weight)
Mass = amount of ‘stuff’ in an object (same value anywhere in the universe)
Weight = the force acting on an object due to gravity (so its different on different planets)
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8
Q

What is the equation that links weight (force), mass, and gravitational field strength?

A

Weight (force) (N) = Mass (kg) x Gravitational Field Strength (N/kg)

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9
Q

What is a free body diagram?

A

Shows all the forces acting on an object with different sized arrows to show strong/weak forces

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10
Q

Define resultant force

A

The overall force on a point or object. You have horizontal and vertical force that have resultant force in a specific direction depending on which side has a stronger force.

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11
Q

What does it mean when work is done?

A

When a force moves an object through a distance, energy is transferred meaning work is done on the object.

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12
Q

What is the equation for work done?

A

Work done (J) = Force (N) x Distance (m)

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13
Q

How do you use scale drawings to find resultant forces?

A

Draw the scale drawing then measure the distance from start to finish and measure the angle to find the bearing.

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14
Q

What does it mean if something is elastically deformed?

A

It can go back to its original shape and length after the force has been removed meaning it is an elastic object (like a spring)

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15
Q

What is the elastic potential energy store of an object?

A

The energy transferred when work is done to stretch or compress an object.

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16
Q

What is the equation for extension and spring constant?

A

Force (N) = Spring Constant (N/m) x Extension (m)

17
Q

What is the limit of proportionality on an extension-force graph?

A

The maximum force meaning that the extension is no longer proportional to force

18
Q

How can you investigate the link between force and extension? [PRACTICAL]

A

Equipment: weighted stand, fix millimetre ruler and spring on with clamp, add masses to spring, tape to mark end of spring

  • measure natural length of spring
  • add mass to spring + record new length of spring (extension is change in length)
  • repeat by adding more mass
  • when there is big increase in extension this means you have reached the spring’s limit of proportionality.
  • draw graph (should be straight line that then curves at end)
19
Q

What is the equation for elastic potential energy?

A

Elastic Potential energy(J) = 1/2 x spring constant (N/m) x extension (m)

20
Q

What’s the equation for distance?

A

Distance (m) = speed (m/s) x time (s)

21
Q

What is the equation for acceleration?

A

Change in velocity (m/s) = Acceleration (m/s^2) x time (s)

22
Q

What’s the difference between acceleration and deceleration?

A

Deceleration is negative acceleration

23
Q

What is the equation for uniform acceleration?

A

V^2 - u^2 = 2as

Final velocity (m/s) = v
Initial velocity (m/s) = u
Acceleration (m/s^2) = a
Distance (m) = s

24
Q

What do different lines on a distance time graph mean?

A 
Gradient = speed (steeper is faster)
Flat line = stationary
Straight diagonal lines = constant speed
Line curving upwards = accelerating 
Line curving downwards = decelerating
25
Q

What do the lines on a velocity-time graph mean?

A

Gradient = acceleration (steeper is faster)
Flat line = steady speed
Straight diagonal lines = constant acceleration/deceleration
Line curving upwards = increasing acceleration
Line curving downwards = decreasing acceleration
Area under graph = distance travelled

26
Q

What does it mean when falling objects reach terminal velocity?

A

When something first falls gravity is the stronger force meaning it accelerates. As the speed increases so does friction meaning it starts to slow it down until gravity and friction are equal and it falls at constant speed. This means it has reached its terminal velocity.

27
Q

What are Newton’s three laws of motion?

A
  1. You need a resultant force for something to start moving or change direction (one force has to be stronger)
  2. The larger the resultant force the faster it will move (F=ma)
  3. When two objects interact they exert equal and opposite forces onto each other.
28
Q

How can you investigate the effect of mass and force on acceleration? [PRACTICAL]

A

Equipment: trolley with card in middle (interrupts light gate), light gate connected to data logger, pulley at edge of table, hook with mass hanging from pulley, trolley attached to pulley on table behind starting line.
Effect of mass = add mass to trolley, put behind starting line, release, record acceleration, keep mass on hook the same throughout
Effect of force = all mass on trolley then one at time transfer to hook, put trolley behind starting line, release, then record acceleration

29
Q

What is the equation for stopping distance?

A

Stopping distance = thinking distance + braking distance

30
Q

What is the thinking distance affected by?

A

Speed - faster you’re going the further you will travel in time to react
Reaction time - longer reaction time means longer thinking distance

31
Q

What is the braking distance affected by?

A

Speed - faster it’s going the longer it takes for it to stop
Weather + road surface - whether it’s wet, icy, there are leaves, oil or less grip of tyres
Condition of tyres - if they are bald then they can skid
Condition of brakes - worn or faulty means not enough force will be applied

32
Q

How can you measure reaction times using the ruler drop test?

A
  • someone holds ruler for you
  • you have finger and thumb in line with 0cm
  • they drop it without warning and you catch ruler with thumb and finger
  • where you caught it is the distance fallen
  • acceleration is roughly 9.8 m/s^2
  • use v^2 = u^2 + 2as to find final velocity
  • then use change in velocity/acceleration = time (rearrange v/t=a
33
Q

What is the equation for momentum?

A

Momentum (kg m/s) = mass (kg) x velocity (m/s)

34
Q

Define conservation of momentum

A

The total momentum before an event is the same as after the event (e.g. during a collision)

If a moving ball with momentum hit a stationary ball, the stationary ball would start moving and the moving ball would move but slower than before. If you add up the momentum from both balls, it is the same as the beginning.

Momentum before = momentum after

35
Q

What is the equation for change in momentum?

A

Force (N) = change in momentum (kg m/s) / change in time (s)

36
Q

What causes a change in momentum?

A

When a non-zero resultant force act on a moving object it causes the velocity to change meaning there is a change in momentum.
The force causing the change is equal to the rate of change of momentum.

Physics (4 decks)

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