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Wolsey Hall > Physics Module 2 > Flashcards

Physics Module 2 Flashcards

1
Q

What is force?

A

A push or pull on an object.

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2
Q

What does balanced forces mean?

A

The forces on an object are at an equilibrium (they cancel each other out). The velocity of the object will not change.

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3
Q

What does unbalanced forces mean?

A

The object is accelerating or decelerating. (The velocity is changing.)

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4
Q

What does G-force measure?

A

Acceleration

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5
Q

What is Newton’s first law of motion?

A

Inertia - an object’s velocity will not change unless acted on by a force. An object wants to keep doing what it’s already doing.

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6
Q

What is Newton’s second law of motion?

A

F=ma (Force = mass x acceleration). (Net force = force after all other forces have cancelled out.)

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7
Q

What is Newton’s third law of motion?

A

Every action has an equal and opposite reaction.

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8
Q

What is terminal velocity?

A

When the force of weight downwards is matched exactly by the force of air resistance upwards. They cancel each other out and the object remains at a constant velocity.

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9
Q

What is inertia?

A

The resistance to change in velocity.

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10
Q

What is resultant force?

A

The single force two unbalanced forces are equivalent to. (Force of velocity.)

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11
Q

What is the definition of a Newton?

A

The force required to give 1kg an acceleration of 1m/s(2).

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12
Q

Do forces only affect motion?

A

No. They can also affect an object’s shape or volume.

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13
Q

What is static friction?

A

When the force of friction is greater than the push/pull on the object, and so the object does not move.

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14
Q

What is dynamic friction?

A

Friction on an object moving across another. This creates heat.

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15
Q

Which type of friction is greater?

A

Static friction. Once an object starts to move, friction drops.

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16
Q

What is drag?

A

The friction an object experiences moving through a liquid or gas.

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17
Q

On Earth, how many Newtons does a mass of 1kg weigh?

A

9.8N (Rounded to 10N)

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18
Q

What is the formula for calculating weight?

A

W=mg (Weight = mass x gravity)

19
Q

What are the two meanings of g?

A
  1. Gravitational field strength (Newtons per kilogram)
  2. Acceleration of free fall (metres per second squared)
20
Q

Since action and reaction forces occur in pairs, why do they not cancel out?

A

Because the forces in each pair act on different objects, not the same object.

21
Q

What is momentum?

A

An object’s tendency to remain in motion

22
Q

What is the formula for momentum?

A

p=mv (Momentum = mass x velocity)

23
Q

What is impulse?

A

An object’s change in momentum over time (resultant force x time = change in momentum)

24
Q

Are momentum and impulse scalars or vectors?

A

Vectors (force is a vector, so they are too)

25
Q

What formula links force and momentum?

A

resultant force = change in momentum
time
(resultant force = rate of change of momentum)
This is another way of saying F=ma.

26
Q

What is the law of conservation of momentum?

A

When two or more objects act on each other, their total momentum remains constant (provided no external forces are acting).

27
Q

How do you figure out the velocity of two objects after a collision?

A
  1. You figure out each of their velocities before the collision (since they’re moving in opposite directions, one should be positive and the other should be negative - VECTORS!!)
  2. You add them together, giving you the total velocity before the collision
  3. Total momentum = total mass x velocity, so velocity = momentum over mass
  4. Do the division and voila
28
Q

How do you figure out the resultant force in vector scale drawings?

A
  1. You arrange the arrows tip-to-tail in a grid
  2. You complete the triangle and measure the new side (or use Pythagoras)
  3. You measure the angle to find the direction (bearing from north), or use SOHCAHTOA
29
Q

What is centripetal force?

A

The inward force needed to make an object move in a circle. (NOT produced by circular motion, is required for it)

30
Q

What is required for centripetal force?

A

An inwards force that provides the centripetal force. (Examples: String’s tension on a swing-ball. Sun’s gravitational pull on earth. Nucleus’s electrostatic force on electron.)

31
Q

What is centrifugal force?

A

The outwards force of an object moving in a circle that does not experience centripetal force (person inside car/washing machine). Is actually just the inertia of an object/lack of centripetal force, not a real force.

32
Q

What would happen to an object moving in a circular motion is the centripetal force disappeared? (string cut)

A

It would move along a straight line that is a tangent to the circle

33
Q

How do we know centrifugal force is not a real force?

A

We know there is no real outwards force because if there were, if the centripetal force was removed the object would move in a straight line perpendicular to the tangent.

34
Q

What are the three conditions in which more centripetal force would be needed?

A
  1. Mass of object increases
  2. Speed of object increases
  3. Circle’s radius decreases
35
Q

What is the moment of inertia?

A

An object’s resistance to having the speed of its rotation changed

36
Q

What decreases the moment of inertia?

A

Decreasing the average mass around the axis of rotation (pulling arms in = spin faster)

37
Q

Does a change in velocity mean a change in speed or direction?

A

It’s a vector, so either.

38
Q

Why, in circular motion, is an object always accelerating towards the centre of the circle?

A

Because its direction is always changing, so the velocity is always changing, and so it is always accelerating.

39
Q

How can an object accelerate towards a point in a circular motion without getting closer to it?

A

Because it is always moving inwards from the position it would have had if travelling in a straight line.

40
Q

What is a moment?

A

The turning effect of a force

41
Q

What is the formula for the moment of a force?

A

Moment = F x d
(moment of a force about a point = force x perpendicular distance from the point)

42
Q

What is a torque?

A

The moment of a force

43
Q

What is the principle of moments?

A

When an object is in equilibrium (balanced), the total clockwise moment about a point equals the total anticlockwise moment about the same point

44
Q

What are the conditions for equilibrium?

A

The sum of forces in one direction must equal the sum of forces in the opposite direction. Therefore, the principle of moments must apply.

Wolsey Hall (19 decks)

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