# P3.2

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What is a moment and how can it be calculated?
Moment: turning effect of a force. Moment = Force (N) × D (Perpendicular distance from line of action of force to the picot in m). The moment can be increased by increasing the force or distance to the pivot.
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Why is it easier to undo a wheel-nut by pushing on the end of a long spanner than a short one?
As the long spanner increases the distance between the line of action and the pivot.
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How can we make use of a lever to make a job easier?
A lever acts as a force multiplier so that the effort we apply (force we apply) can be much less than the load (the force we’re trying to move).
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What is the centre of mass and when is an object in equilibrium?
The point where the mass of the object can be thought to be concentrated. Any object freely suspended will come to rest with its centre of mass directly below the point of suspension and is then in equilibrium.
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How can you find the centre of mass of a thin irregular sheet of material as follow?
By suspending the thin sheet from a pin held in a clamp stand. Freely suspended so can turn. When it comes to rest, hang a plumbline from the same pin. Mark the position of the plumbline against the sheet. Repeat. Point of intersection =centre of mas
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Where does the centre of mass lie on a symmetrical object?
Along its axis of symmetry. If the object has more than one axis of symmetry, the centre of mass is where the axes of symmetry meet. The centre of mass depends on the shape and sometimes lies outside the object.
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What does the principle of moments state?
An object in equilibrium is balanced, not turning. The total clockwise moment and anticlockwise moment are equal in the moments about any point. Everyday examples i.e. seesaws + balance scales.
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Where does an objects line of action act?
Through the centre of mass. If the line of action of the weight lies outside the base of an object, there will be a resultant moment and the object will tend to topple over.
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How do you increase the stability of an object?
The wider the base of an object and the lower its centre of mass, the further it has to tilt before the line of action of the weight moves outside the base and so the more table it is.
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How do you calculate the pressure of an object?
Pressure (Pa/Pascals or N/m2) = Force (N) ÷ A (Cross sectional area at right angles to the direction of the force in m2).
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What properties of a liquid make it useful in a hydraulic system?
Liquids are virtually incompressible + the pressure in a liquid is transmitted equally in all directions. This means that a force exerted at 1 point on a liquid will be transmitted to other points in the liquid.
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What does the force exerted by a hydraulic pressure system depend on?
The force exerted on the system. The area of the cylinder on which this force acts on and the area of the cylinder that exerts the force.
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How can a small effort be used to move a large load using a hydraulics system?
The use of different cross-sectional areas on the effort and load sides of a hydraulic system means that the system can be used as a force multiplier.
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What is centripetal acceleration?
When an object moves in a circle it is continuously changing direction, so its continuously changing velocity. This means that it is accelerating = centripetal acceleration.
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What is centripetal force?
An object only accelerates when a resultant force acts on it. This force is called centripetal force + always acts towards the centre of the circle. When it stops acting, the object will continue to move in a straight line to the circle.
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How does the centripetal force needed to make an object perform circular motion increase?
As the mass of the object increases. As the speed of the object increases. As the radius of the circle decreases. Centripetal force isn’t a force in its own right but is provided by another force i.e gravitational force, electric force or tension.
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What does a simple pendulum consist of?
A mass (called a bob) suspended on the end of a string. When the bob is displaced to one side + let go, the pendulum oscillates back and forth, through the equilibrium position (rest position). The pendulum is an example of oscillating motion.
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What is the time period of the oscillation for one complete cycle?
The time taken from the highest position on one side to the highest on the other + back to the start position. The time taken between successive passes in the same direction through the equilibrium position.
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How do we measure the time period of a pendulum + what’s the frequency + amplitude of the oscillations?
Measure the average time for 20 oscillations and divide the timing by 20. Amp: The distance from equilibrium position to the highest position on either side. Frequency: No. of complete cycles of oscillation per second.
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What is the equation that links frequency and time period?
Time period (s) = 1 / frequency (Hz).
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Why will a playground swing come to rest if not pushed repeatedly?
As the energy is transferred due to friction at the top of the swing due to air resistance.
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## Other cards in this set

### Card 2

#### Front

Why is it easier to undo a wheel-nut by pushing on the end of a long spanner than a short one?

#### Back

As the long spanner increases the distance between the line of action and the pivot.

### Card 3

#### Front

How can we make use of a lever to make a job easier?

### Card 4

#### Front

What is the centre of mass and when is an object in equilibrium?

### Card 5

#### Front

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