P3- Using physics to make things work Flashcards

1
Q

What is a moment?

A

Turning effect of a force.

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2
Q

How can the size of a moment be calculated?

A

M= F x d

M= Moment of force in newton-metres (Nm).

F= Force in N.

d= Perpendicular distance from the line of action of the force to the pivot (m).

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3
Q

How can you increase a moment?

A
  • Increase the force.
  • Increases the distance to the pivot.
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4
Q

What is the centre of mass of an object?

A

The point where the mass of an object can be thought to be concentrated.

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5
Q

What is meant by an object being in ‘equilibrium’?

A

When an object is freely suspended and comes to rest with its centre of mass directly below the point of suspension.

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6
Q

How can you find the centre of mass of a thin irregular sheet of material?

A

1) Suspend sheet from a pin held in a clamp stand.
2) When it comes to rest, hang a plumbline from the same pin.
3) Mark the position of the plumbline against the sheet.
4) Hang the sheet with the pin at another point and repeat procedure at least twice more.
5) The centre of mass is where the lines that marked the position of the plumbline cross.

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7
Q

Where is the centre of mass of a symmetrical object?

A

Along the axis of symmetry.

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8
Q

What is the principle of moments?

A

Sum of anticlockwise moment= Sum of clockwise moment.

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9
Q

Aimie sits 2m from the centre of a seesaw. Leo weighs twice as much as Aimie.

How far from the centre must he sit to balance the seesaw?

A

1m.

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10
Q

If someone sits in the centre of a seesaw, the moment about the pivot is zero.

Why?

A

Because the perpendicular distance to the pivot is zero.

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11
Q

How can the stability of an object be increased?

A
  • Making the base as wide as possible.
  • Making the centre of mass as low as possible.
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12
Q

Why does an object topple over?

A

If the line of action of its weight is outside its base.

If the resultant moment about its point of turning is not zero.

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13
Q

Why does hanging heavy bags from the handle of a pushchair make it more likely to topple over?

A

The bags raise the centre of mass so the pushchair will not have to tilt so far before the line of action of the weight moves outside the base.

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14
Q

How can pressure be calculated?

A

P= F/A

P= Pressure in pascals (Pa or N/m2).

F= Force (N).

A= Area (m2).

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15
Q

What does the force exerted by a hydraulic pressure system depend on?

A
  • Force exerted on system.
  • Area of cylinder on which this force acts on.
  • Area of cylinder that exerts force.
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16
Q

What properties of a liquid make it useful in a hydraulic system?

A

Liquids are virtually incompressible, and the pressure in the liquid is transmitted equally in all directions.

17
Q

What is the velocity of an object moving in a circle at a constant speed?

A

Velocity is continually changing as the object’s direction is continually changing.

18
Q

What is centripetal acceleration?

A

The acceleration towards the centre of the circle of an object moving round the circle.

19
Q

What is centripetal force?

A

The resultant force acting towards the centre of the circle when an object is moving in a circle.

20
Q

How can centripetal force increase?

A
  • If the mass of object increases.
  • If the speed of object increases.
  • If the radius of the circle decreases.
21
Q

A student is whirling a conker around on a piece of string, in a horizontal circle.

What force provides the centripetal force?

A

Tension in the string.

22
Q

What does the time period of a simple pendulum depend on?

A

The length of the pendulum.

Longer pendulums have greater time periods than shorter pendulums.

23
Q

How does a simple pendulum work?

A

A simple pendulum consists of a mass (called a bob) suspended on the end of a string.

When the bob is displaced to one side and let go, the pendulum oscillates back and forth through the equilibrium position.

24
Q

What is the amplitude of the oscillation in a pendulum?

A

The distance from the equilibrium position to the highest position on either side.

25
Q

What is the time period for a pendulum?

A

The time taken for a pendulum to swing from one side to the other and then back again to its original position.

26
Q

What is the frequency of a pendulum?

A

Number of complete swings (cycles of oscillation) per second.

27
Q

How can the time period of a pendulum be calculated?

A

T= 1/f

T= Time period (s).

f= Frequency (Hz).

28
Q

How can the time period of a pendulum be measured?

A

Measure the average time for 20 oscillations and divide the timing by 20.

29
Q

A playground swing is an example of an oscillating motion. If not pushed repeatedly, why will the swing come to rest?

A

Because energy is transferred due to friction at the top of the swing and air resistance.

30
Q

What force provides the centripetal force as a car travels around a bend in the road?

A

Friction.

31
Q

A racing car should not roll over when racing.

Suggest two reasons why.

A
  • Low centre of mass.
  • Wide base.
32
Q

The bus will topple over if the ramp is tilted at too great an angle.

Explain why (2 marks).

A

The line of action of the weight lies outside the base (1) so there is a resultant moment acting on the bus (1).

33
Q

What is the unit for a moment?

A

Nm.