13. Oscillations

Question 1

What happens it an object is experiencing simple harmonic motion?

Answer 1

• It experiences a restoring force which acts towards the centre of equilibrium.
• Its force is directly proportional to the object’s distance from equilibrium.

Question 2

What is amplitude?

Answer 2

The maximum displacement of an oscillating system

Question 3

What is time period?

Answer 3

Time take for one full cycle of an oscillating system.

e.g.
Equilibrium to amplitude.
Then amplitude to equilibrium.

Question 4

What is the restoring force?

Answer 4

A force that acts towards the equilibrium.

Question 5

What is true about the acceleration of an object experiencing SHM?

Answer 5

It’s acceleration is directly proportional to is displacement and is in the opposite direction.

a = -ω²x

Question 6

What is angular velocity?

Answer 6

The angle an objects moves through per unit time.

ω = 2πf

Question 7

What effect the time period of these simple harmonic systems?

• Simple pendulum
• Mass-spring system

Answer 7

Simple pendulum: mass and length of spring.

• Mass-spring system:
  mass and spring constant.

Question 8

Describe the graph of displacement against time of a SHsystem.

Answer 8

Sinusoidal

- starting at (+)amplitude.

Question 9

Describe the graph of velocity against time of a SHsystem.

Answer 9

Sinusoidal
- starting at 0

(its the gradient function of dis-time)

Question 10

Describe the graph of acceleration against time of a SHsystem.

Answer 10

Sinusoidal
- starting at (-)amplitude.

(its the gradient function of velo-time)

Question 11

What is resonence?

Answer 11

Where the amplitude of an oscillating system increases due to gaining an increased amount of energy from the driving force.

Question 12

When does resonance occur?

Answer 12

When the driving force is equal to the natural frequency of the system.

Question 13

How do you decrease the effects of resonance?

Answer 13

Dampening.

Question 14

What is dampening?

Answer 14

• Where a force acts on an oscillating system and energy is lost from the system to its environment.
• Leading to a reduced amplitude.

Question 15

When can oscillating systems lose/gain energy?

Answer 15

When an external force acts on it.

Question 16

What is true of an undamped system?

Answer 16

• There are no external forces acting.
• No energy is lost to the environment.
• Total energy of the system remains constant.

Question 17

Describe the change in energy of a SHsystem.

Answer 17

• At amplitude the system has maximum potential energy.
• As moves to equilibrium, PE is converted to kinetic energy.
• At centre of oscillation KS is at a maximum.

Question 18

What are free vibrations?

Answer 18

• When there is no external force that is continuously acting on a system.
• Thus the system oscillates at its natural frequency.

Question 19

What are force vibrations?

Answer 19

• When a system experiences an external driving force which causes it to oscillate.
• Its frequency is known as the driving frequency.

Question 20

What are the three types of damping?

Answer 20

• Over.
• Critical.
• Under.

Question 21

What is under damping?

Answer 21

• Where the amplitude gradually decreases by small amounts each oscillation.
• Graph of diminishing sinusoidal wave.

Question 22

What is critical damping?

Answer 22

• Where the amplitude reduces to zero in the shortest possible time without oscillating.
• Starts at maximum and curves to zero rapidly.

Question 23

What is over-damping?

Answer 23

• Where the amplitude reduces slower than critical damping but without any additional oscillations.
• Starts at zero and curves to zero over time.

Question 24

What happens to the amplitude once the degree of dampening increases?

Answer 24

It decreases.

Question 25

What is a ductile material?

Answer 25

One that can undergo a large amount of plastic deformation before fracturing.

Question 26

Why can a ductile material be used in dampening?

Answer 26

• it can reduce the amplitude of oscillation
• because energy is used to defor the material.
• decreasing the KE of the system.
• so decreasing the amplitude of oscilation.