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A level physics > 4 - Forces in action > Flashcards

4 - Forces in action Flashcards

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1
Q

What is mass?

A

A physical property of an object which describes how much matter it contains.

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2
Q

Define net force.

A

The sum of all of the forces acting on an object.

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3
Q

What does a net force cause?

A

Acceleration in the direction of the force.

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4
Q

What is weight?

A

The gravitational force acting on an object.

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5
Q

What is an object’s centre of mass?

A

A point in an object through which its entire weight can be thought to act.

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6
Q

How would you carry out an experiment to determine an object’s centre of mass?

A
  • Hang object - free to spin
  • Hang plumb line and mark line
  • Repeat in two other positions
  • Point where lines cross is centre of mass.
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7
Q

What is each force represented by in a free body diagram?

A

A labelled arrow, proportional to the size of the force.

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8
Q

What is friction?

A

The force that arises when two surfaces rub against each other.

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9
Q

What is drag?

A

The resistive force acting on an object that is travelling through a fluid.

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10
Q

What is tension?

A

The force within a stretched cable or rope.

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11
Q

What is upthrust?

A

An upwards buoyancy force acting on a liquid.

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12
Q

What is normal contact force?

A

A force arising when one object rests against another object.

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13
Q

What is drag proportional to?

A

velocity squared x surface area

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14
Q

What is the drag force experienced by objects travelling through air commonly called?

A

Air resistance

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15
Q

Define terminal velocity.

A

When an object stops accelerating and has a constant velocity because the drag is equal and opposite to its weight.

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16
Q

Describe how a falling object reaches terminal velocity.

A
  • At release, acceleration is equal to g, downward force = mg, net force = mg
  • As object accelerates, velocity increases, downward force = mg, upwards force = D, net force = mg - D
  • Eventually, drag becomes equal to weight and so net force = 0, drag cannot increase because speed is no longer increasing
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17
Q

What is the only factor that can affect an objects terminal velocity when it is already travelling at terminal velocity?

A

Surface area

e.g. parachute

18
Q

What is a moment?

A

The turning effect of a force around a point.

19
Q

How do you calculate a moment?

A

Force x distance from pivot

20
Q

What must you always ensure (and sometimes have to calculate) before calculating a moment?

A

That the force and the distance are perpendicular.

21
Q

What is the principle of moments?

A

When a body is at rotational equilibrium, the sum of the clockwise moments must be equal to the sum of the anticlockwise moments.

22
Q

What is a couple?

A

A pair of equal, parallel forces acting in opposite directions.

23
Q

What is torque?

A

The moment of a couple.

24
Q

How do you calculate torque?

A

One of the forces x distance between forces.

25
Q

What does coplanar mean?

A

All the forces lie in the same plane e.g. 2d

26
Q

Define density.

A

Mass per unit volume.

27
Q

Define pressure.

A

Normal force exerted per unit area.

28
Q

How could you determine the volume of a irregularly shaped object?

A
  • Fill measuring cylinder with known volume of liquid

- Push object under water level and see how much the volume changed by

29
Q

What is a fluid?

A

A substance that flows. Gases or liquids

30
Q

What is the equation for pressure under a column of liquid?

A

P = hpg

31
Q

Does the cross-sectional area of the column of water affect the pressure?

A

NO

32
Q

What is pressure under water proportional to?

A

The depth below the water, h.`

33
Q

In what direction is pressure the same at a certain depth under water?

A

All directions

34
Q

What is pressure caused by?

A

Particles moving and colliding with objects.

35
Q

What must you always remember to include when calculating pressure underwater?

A

The pressure exerted by the atmosphere above the water.

36
Q

What is upthrust caused by?

A

A difference in pressure above and below an object.

37
Q

When will an object float?

A

If the upthrust force is greater than the weight of the object.

38
Q

How do you calculate upthrust?

A

F = pxgA

pressure below - pressure above

Pb = pgh + pgx Pa = pgh

P = pgh + pgx - pgh = pgx

p = F/A F = pA

F = pgxA

39
Q

What does Archimedes’ Principle state?

A

The upthrust force exerted on a body is equal to the weight of fluid that the object displaces.

40
Q

What conditions (density) must be met in order for an object to float?

A

The average density of the object must be less than the density of the fluid.

A level physics (26 decks)

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