Using Physics to Make Things Work

Question 1

What is a moment?

Answer 1

The turning effect of a force (on an object)

Question 2

What are moments measured in?

Answer 2

Newton metres Nm

Question 3

What is the line of action?

Answer 3

The line along which a force acts

Question 4

In the equation M = F x d, what does d stand for?

Answer 4

The perpendicular distance from the line of action to the pivot. It is measured in metres

Question 5

What can be done to increase the moment?

Answer 5

Either:

Increase the force

Increase the distance

Question 6

When using a lever, what is the name of the force we are trying to move?

Answer 6

The load

Question 7

When using a lever, what is the name of the force we are applying to the lever?

Answer 7

The effort

Question 8

What is mean by a force multiplier?

Answer 8

The effort applied is less than the load

Question 9

What is mean by a distance multiplier?

Answer 9

A small distance is moved on the load side of the fulcrum and a large distance is moved on the other as a result.

Question 10

What is the centre of mass?

Answer 10

The point where an objects mass can be thought to be concentrated

Question 11

If an object is freely suspended where will its centre of mass lie?

Answer 11

Directly below the point of suspention

Question 12

What is equilibrium?

Answer 12

The state of an object when it is at rest

Question 13

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

Answer 13

• 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

Question 14

What does the position of the centre of mass depend upon?

Answer 14

The shape of the object. Subsequently, it can sometimes lie outside the shape of the object

Question 15

Where does the centre of mass lie in a symetrical object?

Answer 15

Along the axis of symmetry. If the object has more than one axis of symmetry, the centre of mass is where the axes meet

Question 16

If an object is in equilibrium, it is…

Answer 16

balanced and not turning

Question 17

What is the total clockwise moment equal to (in an object in equilibrium)?

Answer 17

The total anti-clockwise moment

Question 18

State some everyday examples of the principle of moments

Answer 18

Seesaws and balance scales

Question 19

How is the stability of an object increased?

Answer 19

By making its base as wide as possible and its centre of mass as low as possible

Question 20

Where does the line of action of the weight of an object act?

Answer 20

Through its centre of mass

Question 21

If the line of action of the weight lies outside the base of an object, what will happen?

Answer 21

There will be a resultant moment and the object will tend to topple over (although not always)

Question 22

The wider the object, the lower its centre of mass. This means…

Answer 22

the further it has to tilt before the line of action of weight moves outside the base

Question 23

What two things can make an object topple?

Answer 23

If the line of action of weight is outside the base

OR

if the resultant moment about its point of turning is not 0

Question 24

What are pascals (Pa) equal to?

Answer 24

N/m²

Question 25

In the equaltion *P = F/A*, what is *A*?

Answer 25

The cross-sectional area at right angles to the direction of the force. It is measured in m²

Question 26

How does the pressure of a fluid act?

Answer 26

Equally in all directions

Question 27

Can you compress liquids?

Answer 27

No.

Question 28

How do hydraulic systems use pressure?

Answer 28

They use the pressure in a fluid to exert a force

Question 29

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

Answer 29

* 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

Question 30

What allows a hydraulic system to act as a force multiplier and what does this mean it can be used to do?

Answer 30

**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.

Question 31

What causes centripetal acceleration?

Answer 31

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**.

Question 32

What is centripetal force?

Answer 32

The resultant force towards the centre of a circle acting on an object moving in a circular path.

Question 33

What happens if the centripetal force stops acting?

Answer 33

The object will continue to move in a straight line at a tangent to the circle.

Question 34

What is centripetal acceleration?

Answer 34

The acceleration of an object moving in a circle at a constant speed. It always acts towards the centre of the circle.

Question 35

What causes the centipetal force needed to make an object perform circular motion increase?

Answer 35

* The **mass** of the object **increases** * The **speed** of the object **increases** * The **radius** of the circle **decreases**

Question 36

Give an example of oscillating motion.

Answer 36

A pendulum moving to and fro along the same line

Question 37

Define oscillating motion.

Answer 37

The motion of any object that moves to and fro along the same line (like a pendulum).

Question 38

What is a simple pendulum?

Answer 38

A pendulum consisting of a small, spherical bob (mass) suspended by a thin string from a fixed point

Question 39

What is the equilibrium position?

Answer 39

The position of a pendulum when it stops moving

Question 40

What is a bob?

Answer 40

The mass at the end of a pendulum

Question 41

What happens when the bob is displaced to one side (and let go of)

Answer 41

The pendulum oscillates back and forth through the equilibrium position

Question 42

What is the amplitude of an oscillation?

Answer 42

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**.

Question 43

What does the time period of the oscillation depend on?

Answer 43

The length of the pendulum

Question 44

How does the length of the pendulum effect the time period of its oscillation?

Answer 44

As the length increases, so does the time period (i.e. bigger pendulums take longer to swing)

Question 45

What is the frequency of oscillations?

Answer 45

The number of complete cycles of oscillation per second

Question 46

What is a playground swing an example of?

Answer 46

Oscillating motion

Question 47

What happens if a swing is not pushed repeatedly and why?

Answer 47

It will come to rest because **energy is transfered** at the **top of the swing** due to **friction** and due to **air resistance**.