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Higher Physics > Forces, Energy and Power > Flashcards

Forces, Energy and Power Flashcards

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1
Q

Describe what is meant by ‘friction’.

A

A force which opposes the motion of an object.

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2
Q

Name one type of friction.

A

Air resistance/drag

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3
Q

If two forces act in the same direction, should you add or subtract them to find the resultant force?

A

Add

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4
Q

If two forces act in opposite directions, should you add or subtract them to find the resultant force?

A

Subtract

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5
Q

Describe what is meant by an object having ‘balanced forces’ acting on it.

A

The object has the same force acting on it in two directions.

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6
Q

Draw a free-body diagram of a block with balanced forces acting on it.

A

Any object with the same value of force on opposing sides.

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7
Q

Describe what is meant by an object having ‘unbalanced forces’ acting on it.

A

The object has a larger force in one direction than the other.

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8
Q

Draw a free-body diagram of a block with unbalanced forces acting on it.

A

Any object with different values of force on opposing sides.

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9
Q

Define ‘Newton’s 1st Law’.

A

An object will remain at rest or move at a constant speed in a straight line unless acted on by an unbalanced force.

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10
Q

What can be said about the forces acting on an object if it moves at a constant speed?

A

The forces are balanced.

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11
Q

In terms of Newton’s 1st Law, describe what would happen to a passenger not wearing a seatbelt in the event of a crash.

A

They would continue to move forward, at the original speed before the crash, into the dashboard/steering wheel etc.

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12
Q

Define ‘Newton’s 2nd Law’.

A

When the forces acting on an object are unbalanced, the object will accelerate in the direction of the unbalanced force.

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13
Q

Write down the equation relating unbalanced force, mass and acceleration.

A

Fu=ma

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14
Q

State the symbol and units for unbalanced force.

A

F, N

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15
Q

State the symbol and units for mass.

A

m, kg

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16
Q

Draw a free-body diagram to show the four forces acting on an aeroplane.

A

Weight, drag, thrust, lift

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17
Q

Define ‘Newton’s 3rd Law’.

A

If an object A exerts a force on object B, then B exerts an equal but opposite force on A. OR For every action there is an equal and opposite reaction.

18
Q

The action and reaction forces for Newton’s 3rd Law are also known as ___________ ________.

A

Newton pairs

19
Q

Give two examples of newton pairs (i.e. action and reaction forces).

A

Force of driver on seatbelt and force of seatbelt on driver/balloon pushing air out and air pushing back on balloon/rocket engines pushing hot gases downwards and hot gases pushing back on rocket/cannon firing cannonball outwards and cannonball exerting a force back on cannon/force of foot kicking ball and force of ball back on foot

20
Q

When a car crashes, the driver moves against the seatbelt, exerting a force on it (action force). State the reaction force for this newton pair.

A

The seatbelt locks in place and exerts a force back on the driver.

21
Q

When a rocket launches, the rocket engines push hot gases downwards (action force). State the reaction force for this newton pair.

A

Hot gases push back on the rocket (upwards).

22
Q

Explain, in terms of forces, why a rocket will eventually move upwards during launch.

A

When the thrust from the engines becomes greater than the weight, an unbalanced force upwards is produced, causing the rocket to accelerate upwards.

23
Q

As a rocket travels upwards, what happens to the air resistance acting on it as its speed increases?

A

It increases

24
Q

As a rocket uses up fuel, what happens to its weight?

A

It decreases

25
Q

As a rocket gets further away from the Earth’s surface, what happens to its weight?

A

It decreases

26
Q

Draw a free-body diagram to show the forces acting on a rocket during launch.

A

Drag, thrust, lift, weight

27
Q

Describe what is meant by a ‘connected system’.

A

When two or more objects are physically joined in some way.

28
Q

Describe what is meant by ‘tension’.

A

The pulling force of a string, rope, cable or chain.

29
Q

If a mass is suspended (hanging) from a point via some string, in which direction will the tension in the string act?

A

Towards the point it is being suspended from.

30
Q

Describe what is meant by ‘free-fall’.

A

An object that is accelerating towards the ground due to the influence of gravity alone.

31
Q

Explain how a skydiver in free-fall will reach terminal velocity.

A

When a skydiver jumps out of a plane, they are in free-fall. Air resistance/drag increases as they accelerate downwards, and eventually the weight of the skydiver downwards and the drag force upwards become balanced. The skydiver now travels at a constant speed i.e. terminal velocity.

32
Q

Define the term ‘terminal velocity’.

A

For an object in free-fall, a constant speed is reached when the upward force on the object (air resistance) is balanced by the downward force on the object (weight).

33
Q

Sketch a velocity-time graph for a free-falling skydiver. No numerical values are required on the axes.

A

Axes with a sloping acceleration till it reaches a constant speed then a rapid deceleration till steady speed.

34
Q

Describe what is meant by ‘mass’.

A

The quantity of particles that make up an object. It is a scalar quantity.

35
Q

Describe what is meant by ‘weight’.

A

The force due to gravity acting on an object. It is a vector quantity.

36
Q

Explain the difference between mass and weight, including their units.

A

Mass is the quantity of particles that make up an object, measured in kilograms, whereas weight is the force due to gravity acting on an object, measured in newtons.

37
Q

Write down the equation relating weight, mass and gravitational field strength.

A

w=mg

38
Q

State the symbol and units for weight.

A

W, N

39
Q

State the symbol and units for gravitational field strength.

A

g, N/kg

40
Q

Name the two forces acting on a person who is standing on a set of scales in a lift.

A

Weight, reaction force

41
Q

For a person standing on a set of scales in a lift, what is the reaction force equivalent to?

A

The reading on the scales.

42
Q

Sketch a free-body diagram for a person standing on a set of scales in a stationary lift.

A

Higher Physics (5 decks)

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