Using Physics to Make Things Work Flashcards
What is a moment?
The turning effect of a force (on an object)
What are moments measured in?
Newton metres Nm
What is the line of action?
The line along which a force acts
In the equation M = F x d, what does d stand for?
The perpendicular distance from the line of action to the pivot. It is measured in metres
What can be done to increase the moment?
Either:
Increase the force
Increase the distance
When using a lever, what is the name of the force we are trying to move?
The load
When using a lever, what is the name of the force we are applying to the lever?
The effort
What is mean by a force multiplier?
The effort applied is less than the load
What is mean by a distance multiplier?
A small distance is moved on the load side of the fulcrum and a large distance is moved on the other as a result.
What is the centre of mass?
The point where an objects mass can be thought to be concentrated
If an object is freely suspended where will its centre of mass lie?
Directly below the point of suspention
What is equilibrium?
The state of an object when it is at rest
How can you find the centre of mass of a thin, irregular sheet of a material?
- Suspend the shape from a pin held in a clamp stand. Because it is freely suspended it able to turn
- When it comes to rest, hand a plumbline from the same pin.
- Mark the position of the plumbline against the sheet
- Hang the sheet with the pin at another point and repeat.
- The centre of mass is where the lines that marked the position of the plumbline cross
What does the position of the centre of mass depend upon?
The shape of the object. Subsequently, it can sometimes lie outside the shape of the object
Where does the centre of mass lie in a symetrical object?
Along the axis of symmetry. If the object has more than one axis of symmetry, the centre of mass is where the axes meet
If an object is in equilibrium, it is…
balanced and not turning
What is the total clockwise moment equal to (in an object in equilibrium)?
The total anti-clockwise moment
State some everyday examples of the principle of moments
Seesaws and balance scales
How is the stability of an object increased?
By making its base as wide as possible and its centre of mass as low as possible
Where does the line of action of the weight of an object act?
Through its centre of mass
If the line of action of the weight lies outside the base of an object, what will happen?
There will be a resultant moment and the object will tend to topple over (although not always)
The wider the object, the lower its centre of mass. This means…
the further it has to tilt before the line of action of weight moves outside the base
What two things can make an object topple?
If the line of action of weight is outside the base
OR
if the resultant moment about its point of turning is not 0
What are pascals (Pa) equal to?
N/m2
In the equaltion P = F/A, what is A?
The cross-sectional area at right angles to the direction of the force. It is measured in m2
How does the pressure of a fluid act?
Equally in all directions
Can you compress liquids?
No.
How do hydraulic systems use pressure?
They use the pressure in a fluid to exert a force
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 the force acts upon
- The area of the cylinder which exerts the force
What allows a hydraulic system to act as a force multiplier and what does this mean it can be used to do?
Different cross-sectional areas on the effort and load sides of the system.
Therefore, a small effort can be used to move a large load.
What causes centripetal acceleration?
When an object moves in a circle it is continually changing direction, so it is continuously changing velocity. In other words, it is accelerating.
This acceleration is called the centripetal acceleration.
What is centripetal force?
The resultant force towards the centre of a circle acting on an object moving in a circular path.
What happens if the centripetal force stops acting?
The object will continue to move in a straight line at a tangent to the circle.
What is centripetal acceleration?
The acceleration of an object moving in a circle at a constant speed. It always acts towards the centre of the circle.
What causes the centipetal force needed to make an object perform circular motion increase?
- The mass of the object increases
- The speed of the object increases
- The radius of the circle decreases
Give an example of oscillating motion.
A pendulum moving to and fro along the same line
Define oscillating motion.
The motion of any object that moves to and fro along the same line (like a pendulum).
What is a simple pendulum?
A pendulum consisting of a small, spherical bob (mass) suspended by a thin string from a fixed point
What is the equilibrium position?
The position of a pendulum when it stops moving
What is a bob?
The mass at the end of a pendulum
What happens when the bob is displaced to one side (and let go of)
The pendulum oscillates back and forth through the equilibrium position
What is the amplitude of an oscillation?
The time taken for the pendulum to complete one full cycle. This is:
- The time taken for the bob to go from the highest position on one side to the highest position on the other an back
OR:
- The time taken between successive passes in the same direction through the equilibrium position.
What does the time period of the oscillation depend on?
The length of the pendulum
How does the length of the pendulum effect the time period of its oscillation?
As the length increases, so does the time period
(i.e. bigger pendulums take longer to swing)
What is the frequency of oscillations?
The number of complete cycles of oscillation per second
What is a playground swing an example of?
Oscillating motion
What happens if a swing is not pushed repeatedly and why?
It will come to rest because energy is transfered at the top of the swing due to friction and due to air resistance.
