Mechanical Systems

Question 1

Describe what Aristotle, Galileo and Newton did to develop mechanical systems?

Answer 1

• Aristotle (384 – 322 BC): Theories were accepted for more than 1000 years. Based on philosophy. Believed the Earth was the centre of the universe.
• Galileo (1564 – 1642): Italian physicist and astronomer who disagreed with Aristotle. Used scientific observation to disprove much of Aristotle’s teachings and followed Copernicus’ theory that the Earth and other planets revolved about the Sun.
• Newton (1642 – 1727): The father of modern physics. His laws of motion are still used today and have been proven to apply in all but a few exceptional situations.

Question 2

When is a force applied?

Answer 2

A force is applied whenever an object is pushed, pulled, twisted, rotated or deformed.

Question 3

What is the first law of Newtons laws of motion? What is an example of this law?

Answer 3

First Law (Inertia): A body remains in a state of rest, or continues with uniform motion, in a straight line, until it is acted upon by a force. This is also known as inertia, for example if you are standing on a moving bus and it slows down, you want to keep moving forward. Likewise, if the bus has stopped and starts again you want to keep still

Question 4

What is the second law of Newtons laws of motion? What is an example of this law?

Answer 4

Second Law (F = ma): An object changes velocity (accelerates) when a force acts on it (F=ma)

Question 5

What is the third law of Newtons laws of motion? What is an example of this law?

Answer 5

Third Law (Action and Reaction): For every action there is an equal and opposite reaction

Question 6

Can multiple forces be applied to the same object? If they can, are they added to create what type of force? Which of Newtons law is this net force applied to?

Answer 6

Multiple forces can be applied to the same object. These multiple forces can be added to obtain the resultant or net force. It is the net force that is applied to Newton’s Second Law.

Question 7

If the net force is equal to zero, what is the object said to be in? Is it accelerating?

Answer 7

If the net force is equal to zero, the object is said to be in equilibrium and is not accelerating.

Question 8

What can force be described as? What do forces change the state of?

Answer 8

Forces – a force can be described as a push or a pull. These actions change the state of motion of bodies upon which they act.

Question 9

Name the 5 different forces

Answer 9

Compression
Tension
Bending (Refraction)
Torsion
Shear

Question 10

Explain the different forces, compression, tension, bending (refraction), torsion and shear and give an example

Answer 10

• Compression – squashing effect. When people sit on a chair
• Tension – stretching force, when you stretch a lolly snake
• Bending (Refraction) – bending forces like bending a diving board
• Torsion – twisting or turning force, when you twist a towel to dry it
• Shear – cutting force (like scissors)

Question 11

What is motion

Answer 11

Motion – the act of changing position

Question 12

Name the four different types of motion

Answer 12

Linear, rotary, reciprocating and oscillating

Question 13

Explain linear motion and give an example

Answer 13

Linear motion occurs in a straight line (a car travelling at constant speed or a bullet fired from a rifle), straight line motion in one direction on an axis such as elevators

Question 14

Explain rotary motion and give an example

Answer 14

Rotary motion causes an object to follow a circular path, circular motion or spinning in one direction such as bike pedals, fishing reels fans or propellers (the Earth spinning on its axis, a charged particle moving in a magnetic field or a turbine blade).

Question 15

Explain reciprocating motion and give an example

Answer 15

Reciprocating motion is caused by a mechanism (the piston in a cylinder, the needle in a sewing machine, the coil in a loudspeaker), back and forth continuous straight line motion on an axis such as pistons, sewing machine jig saw

Question 16

Explain oscillating motion and give an example

Answer 16

Oscillating motion occurs when an object is attempting to return to an equilibrium position after a disturbance (the ground after an earthquake, a pendulum, vehicle suspension), swinging back and forth motion like a pendulum or swing

Question 17

What are the formulas for work, power, mechanical advantage, velocity ratio and efficiency

Answer 17

Work is a measure of energy used, (work = force x distance), - W=F d
Power is the rate at which energy is used or produced (power = work / time), - P=W/t
Mechanical advantage is a ratio of forces, (mechanical advantage = load/effort), - MA=load/effort
Velocity ratio compares the distances moved by the load and effort, (velocity ratio = effort distance/load distance), - VR=effort dist/load dist
Efficiency measures how effectively energy is used (efficiency = mechanical advantage / velocity ratio) - efficiency=MA/VR

Question 18

Can devices be used to change the input and output motion? What is an example?

Answer 18

Yes, example is gears

Question 19

What are the 3 components a lever has?

Answer 19

All levers have three components: the fulcrum, the load and the effort

Question 20

Explain the three classes of lever and give an example of each

Answer 20

There are three types of levers:
* Class 1: pivot in the middle, the effort is applied on one side of the pivot and the load on the other side the fulcrum is between the load and effort (see-saw, crowbar, scissors)
* Class 2: the load is in the middle, the effort is applied to one side pf the load and the pivot is located on the other side, the load is between the fulcrum and effort (wheelbarrow, nutcracker, bottle opener)
* Class 3: the effort is in the middle, the pivot on one side and the load on the other side, the effort is between the fulcrum and load (broom, pair of tweezers)

Question 21

What is mechanical advantage? What is the formula?

Answer 21

Mechanical advantage is a ratio of forces. It is how much more power you gain
Formula is:
(mechanical advantage = load/effort), - MA=load/effort

Question 22

What is the VR formula for levers?

Answer 22

VR= distance of effort from fulcrum / distance of load from fulcrum

Question 23

What is a gear? When it meshes together, what does it do?

Answer 23

A gear is a simple machine (the wheel), it has teeth cut into the circumference.

Two gears mesh together with one driving another without any slipping

Question 24

What size can gears be?

Answer 24

Gears can be almost any diameter and can be assembled into complex gear trains to achieve the desired speed ratio

Question 25

What are the two gears in the system called?

Answer 25

In any set of gears there will be a driver gear and the driven gear

Question 26

Explain the difference between the driven and driving gears and in a gear set with only two gears, if the driven gear is rotating clockwise, what direction would the driving gear be rotating?

Answer 26

• The driver gear is the gear that is directly given force to spin it whereas the driven gear eventually moves because of the driver gear.
• The driving gear would be rotating counter-clockwise.