Section 6 part 2 - Further mechanics and thermal physics (circular and sh motion)

Question 1

Define uniform circular motion

Answer 1

An object rotating at a steady speed

Question 2

Why do you accelerate when moving at a constant speed around a circle?

Answer 2

Velocity is continually changing due to change in direction. If velocity changes, there must be an acceleration as acceleration is rate of change of velocity

Question 3

Which direction does the velocity act on an object in uniform circular motion?

Answer 3

Along the tangent to the circle at that point

Question 4

Which direction does the centripetal force act on an object in uniform circular motion?

Answer 4

Towards the centre

Question 5

Why does the acceleration of an object in uniform circular motion act towards the centre of the circle?

Answer 5

Because the change in direction of the velocity is towards the centre of the circle, so the acceleration acts towards the centre of the circle

Question 6

What causes an object to move around on a circular path?

Answer 6

Being acted upon by a resultant force

Question 7

What is a centripetal force?

Answer 7

The resultant force causing an object to move around a circle at constant speed

Question 8

What is the centripetal force acting on a car when going around a roundabout?

Answer 8

The sideways friction between the vehicle’s tyres and the road surface

Question 9

State the difference in friction for a car going around a banked track vs non banked track

Answer 9

Banked track has no sideways friction

Non-banked track has sideways friction

Question 10

Why do banked tracks not have sideways friction for a vehicle going around it?

Answer 10

Centripetal force is given by the support forces of the tyre

Question 11

How can you get a velocity time graph from a displacement time graph?

Answer 11

Differentiate the graph

Question 12

How can you get an acceleration time graph from a velocity time graph?

Answer 12

Differentiate the graph

Question 13

Define SHM

Answer 13

A type of periodic motion where the acceleration is directly proportional to the displacement and acts in the opposite direction to that of the displacement

Question 14

For a mass spring system oscillating vertically, if you have A at the peak. B at equilibrium and C at the bottom, describe the acceleration and velocity

Answer 14

A - Max acceleration down, 0 velocity
B - 0 acceleration, max velocity
C - max acceleration up, 0 velocity

Question 15

What is the amplitude of an oscillating object?

Answer 15

The maximum displacement of the oscillating object from equilibrium

Question 16

What do you call the oscillations if the amplitude is constant?

Answer 16

Free vibrations

Question 17

What is the time period

Answer 17

Time taken for one complete cycle of oscillation

Question 18

What is the frequency

Answer 18

Number of cycles that pass a point per second

Question 19

What can you conclude when comparing the acceleration time graph against the displacement time graph?

Answer 19

Acceleration is always in the opposite direction to the displacement

Question 20

Which direction does the resultant force act on an oscillating object?

Answer 20

Towards equilibrium

Question 21

What is the restoring force?

Answer 21

The resultant force that acts towards equilibrium

Question 22

What determines the frequency of oscillation of a loaded spring?

Answer 22

Adding extra mass -> increases inertia which means each cycle of oscillation takes longer
Using weaker springs -> Restoring force would be less, acceleration would be less, each cycle of oscillation takes longer

Question 23

What is the restoring force for a spring oscillating vertically that obeys Hooke’s law?

Answer 23

-kx

Question 24

What is another equation for acceleration?

Answer 24

-kx/m

Question 25

How does the tension in the spring vary?

Answer 25

Max when stretched downwards (maximum displacement downwards) = mg + kA Min when compressed upwards (maximum displacement upwards) = mg - kA

Question 26

What are free oscillations?

Answer 26

When an object oscillates with a constant amplitude because there is no friction acting on it

Question 27

What is the equation for SHM energy stored in a spring?

Answer 27

1/2kx^2

Question 28

What is the equation for SHM the total energy of the system?

Answer 28

1/2kA^2

Question 29

What is the equation for SHM kinetic energy

Answer 29

1/2k(A^2-x^2)

Question 30

What are dissipative forces?

Answer 30

Forces causing the amplitude to decrease by dissipating energy of the system to the surroundings as thermal energy

Question 31

When is a motion of an object said to be damped?

Answer 31

When dissipative forces are present

Question 32

When does light damping occur?

Answer 32

When the time period is independent of the amplitude so each cycle takes the same length of time as the oscillations die away

Question 33

What is critical damping?

Answer 33

When the oscillation returns to equilibrium in the shortest possible time without overshooting

Question 34

What is heavy damping?

Answer 34

When the object returns to equilibrium much more slowly than critical damping. No oscillating motion occurs e.g mass spring system in thick oil

Question 35

Describe the 3 types of damping on a displacement time graph

Answer 35

Light - Same time period, but amplitude gradually decreases Critical - Quater of a cos wave Heavy - Negative gradient graph ALL START FROM SAME MAX DISPLACEMENT

Question 36

What is a periodic force?

Answer 36

A force applied at regular intervals

Question 37

What are forced vibrations?

Answer 37

A system undergoes forced vibrations when a periodic force is applied to it

Question 38

When does a system oscillate at maximum amplitude

Answer 38

When the phase difference between displacement and periodic force is 1/2 pi

Question 39

When does a system resonate?

Answer 39

When the periodic force is exactly in phase with the velocity of the oscillating system

Question 40

What is the frequency at maximum amplitude called?

Answer 40

Resonant frequency

Question 41

What happens to the resonance of a system when the damping is lighter?

Answer 41

The maximum amplitude becomes larger at resonance | the closer the resonant frequency is to the natural frequency of the system

Question 42

What is true for a an oscillating system with little or no damping at resonance in terms of frequencies?

Answer 42

Applied frequency of periodic force = natural frequency of system