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GCSE Physics > Using physics to make things work > Flashcards

Using physics to make things work Flashcards

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1
Q

What is the centre of mass?

A

The point through which the whole mass of the object is considered to act. It can be thought of as the point where all the mass is concentrated.

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2
Q

How can the centre of mass for thin, irregular shaped materials with no line of symmetry be found?

A

By using a simple plumb line:

  1. Hang the sheet and a plumb line from one point so both are free to rotate. Mark the position of the plumb line as a vertical line.
  2. Hang the sheet from a different position. Mark the position of the second plumb line.
  3. The centre of mass is the point where the two lines cross. Check this by balancing the sheet on the end of your finger.
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3
Q

What kind of objects are most stable?

A

Those with a wide base and a low centre of mass.

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4
Q

What is the equation that describes the connection between the time period and frequency for a simple pendulum?

A

T = 1 / f
T is the time period in seconds, s
f is the frequency in Hertz, Hz

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5
Q

What does the time period for a pendulum depend on?

A

The length of the pendulum.

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6
Q

Where can applications of pendulums be seen?

A

In children’s playground rides and in fairgrounds.

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7
Q

What is a moment?

A

The turning effect of a force around a pivot point.

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8
Q

What is the equation to calculate the size of a moment?

A

M = F x d
M is the moment of the force in newton metres, Nm
F is the force in Newrons, N
d is the perpendicular distance from the line of action of the force to the pivot in metres, m.

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9
Q

How can the size of a moment be increased?

A
  1. By increasing the value of the force.

2. By increasing the perpendicular distance.

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10
Q

What is a lever?

A

A device that acts like a force multiplier or a distance multiplier.

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11
Q

Give two examples of levers.

A
  1. Lifting a wheelbarrow.

2. Opening a tin of paint with a screwdriver.

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12
Q

What is the law of moments?

A

The idea that when an object isn’t turning, there must be a balance between the total moments of the forces turning the object in a clockwise direction and the total moments of the forces turning the object in an anticlockwise direction.

total clockwise moments = total anticlockwise moments

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13
Q

What equation can be used to show the law of moments?

A

F1 x d1 = F2 x d2

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14
Q

When will an object topple?

A

If the line of action of the force lies outside its base. The weight of the object causes a turning effect, which makes the object topple.

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15
Q

How can stability be increased?

A
  1. By having a lower centre of mass.

2. By having a wider base.

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16
Q

What does the centre of mass represent?

A

A point at which all the mass is said to be concentrated.

17
Q

What is the position of the centre of mass of a rectangle 5 cm long by 3 cm wide?

A

(2.5 cm, 1.5 cm) from any corner, or along the axes of symmetry.

18
Q

An object has forces applied to it but it is not turning. What can be said about the moments on the object?

A

total clockwise movement = total anticlockwise movement

19
Q

What happens when the line of action of the weight of a car lies outside its base?

A

The car will topple over.

20
Q

What is pressure?

A

The force that acts over a particular surface area.

21
Q

What is the formula for pressure?

A

P = F / A
P is the pressure in pascals, Pa
F is the force in Newtons, N
A is the cross sectional area in metres squared, m^2.

22
Q

What is 1 pascal the same as?

A

1 N/m^2

23
Q

How is the pressure in a liquid transmitted?

A

Equally in all directions.

24
Q

If a force is exerted at one point on a liquid, what will happen?

A

The force will be transmitted to other points in the liquid.

25
Q

How can the effort and load on either side of a hydraulic system be altered?

A

By using different cross-sectional areas, which enables to system to be used as a force multiplier.

26
Q

How is an object moving at a constant speed in a circular path moving?

A

It is continuously accelerating towards the centre of the circle.

27
Q

What happens to acceleration when there is a change in velocity of an object moving in a circular direction?

A

There is an associated acceleration. This is because the direction of motion is continuously changing, not the speed.

28
Q

What is the centripetal force?

A

The resultant force causing the acceleration towards the centre of the circle. It is always directed towards the centre of the circle.

29
Q

What is the centripetal force provided by?

A

Friction and tension.

30
Q

How can the centripetal force be increased?

A
  1. By increasing the mass of the object.
  2. By increasing the speed of the object.
  3. By decreasing the radius of the circle.
31
Q

What is the unit of pressure?

A

Pa or N/m^2

32
Q

What is used to transmit the force in a hydraulic system?

A

Liquids.

33
Q

An athlete is undergoing rotational movement just before he throws a hammer. What provides the centripetal force causing the hammer to accelerate in this way?

A

The tension in the wire.

34
Q

In circular motion at constant speed why is there a centripetal acceleration?

A

The velocity of the object changes because its direction changes and acceleration is the rate of change of velocity.

GCSE Physics (4 decks)

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