3.6 Further mechanics and thermal physics

Question 1

What are the requirements for an object to move in circular motion at a constant speed?

Answer 1

Motion in a circular path at constant speed implies there is an acceleration and requires a centripetal force.
(Centripetal force acts towards the center of the circle)

Question 2

Which factors affect the centripetal force?

Answer 2

↑ Mass of the object → ↑ Centripetal force
↑ Speed of the object → ↑ Centripetal force
↑ Radius → ↓ Centripetal force

Question 3

How do you calculate angular speed?

Answer 3

(Velocity) / (radius)
2(pi)f
Only works for radians

Question 4

How do you calculate centripetal acceleration?

Answer 4

(m*v^2)/r
m * ω ^2 * r

Question 5

What are the 2 conditions required for SHM?

Answer 5

The acceleration of a body is proportional to its displacement from the equilibrium position.
The acceleration acts towards equilibrium position.

Question 6

What is the equation for acceleration in SHM?

Answer 6

a = - ω^2 * x

Question 7

What is the equation for displacement in SHM?

Answer 7

x = A * cos(ωt)
Displacement = (amplitude ) * cos[(2 pi * frequency)(time)]

Question 8

What is the equation for velocity in SHM?

Answer 8

v = 土 ω * sqrt [A ^2 - x ^2]

Question 9

What are the 2 main examples of simple harmonic motion?

Answer 9

Pendulums
Mass on a spring

Question 10

What is the equation for maximum speed in SHM?

Answer 10

v = ωA
Velocity = (2pi * frequency) * (acceleration)

Question 11

What is the equation for maximum acceleration in SHM?

Answer 11

a = ω^2 * A
Acceleration = (2pi * frequency)^2 * (acceleration)

Question 12

Which factors affect the period of a pendulum?

Answer 12

The length of the string

Question 13

What happens when a system is under damped?

Answer 13

The system oscillates before coming to a stop.

Question 14

What happens when a system is critically damped?

Answer 14

This is the smallest amount of damping required for a system not to oscillate.

Question 15

What is over damping?

Answer 15

More damping than critically damped.

Question 16

What is free oscillation?

Answer 16

There’s no forces acting other than internal forces
There’s no energy transfer

Question 17

What is forced oscillation?

Answer 17

The oscillator is acted on by a periodic external force
There’s periodic energy transfer

Question 18

What is resonance?

Answer 18

It occurs when driving frequency = natural frequency
The amplitude of vibration increases to maximum leading to maximum energy transfer.

Question 19

What is the definition of internal energy?

Answer 19

The sum of the randomly distributed kinetic energies and potential energies of the particles in a body.

Question 20

How do you increase the internal energy of a system?

Answer 20

When energy is transferred to it by heating or work is done on it.

Question 21

What happens to internal energy when state is changing?

Answer 21

The potential energies of the particles are changing but not the kinetic energies.

Question 22

How can you tell when potential energy has increased?

Answer 22

The distance between the particles will increase.

Question 23

How can you tell when average Ek of the particles has increased?

Answer 23

The temperature of the substance will increase.

Question 24

Describe the internal energy of a solid.

Answer 24

It has the least internal energy as:
The molecules are the closest together an not free to move so, it has less Ep
It has the lowest temperature so it has the lowest Ek.

Question 25

Describe the internal energy of a liquid.

Answer 25

Have more Ek than a solid as the temp is higher. It has more Ep than a solid as bonds have been broken despite distance between particles being the same.

Question 26

Describe the internal energy of a gas.

Answer 26

Has the highest Ek as it has the highest temperature. Largest Ep as the molecules are free from each other and very far apart.

Question 27

What is the specific latent heat of fusion?

Answer 27

The thermal energy released when a liquid changes into a solid, at a constant temperature, per unit mass.

Question 28

What is the specific latent heat of vaporisation?

Answer 28

The thermal energy required to change a liquid into a gas, at a constant temperature, per unit mass.

Question 29

What is specific heat capacity?

Answer 29

The amount of energy required to raise the temperature of a unit mass of a substance by unit temperature.

Question 30

Which is worse, a scald from steam or water, both at 100 C?

Answer 30

Steam is worse Both have the same mass and temperature. Water will cool from 100 C on contact with the skin as thermal energy will be transferred to the skin and the heat of the skin will increase. Steam will remain at 100 C as it condenses and it transfers energy as it changes state and when it cools, it delivers more thermal energy to the skin.

Question 31

What is thermal equilibrium?

Answer 31

For bodies at the same temperature, there’s no net flow of thermal energy.

Question 32

What is brownian motion?

Answer 32

Random motion as a result of collisions with fast, randomly-moving particles in the fluid.

Question 33

What is the evidence for Brownian motion?

Answer 33

Large, heavy smoke particles are moved with Brownian motion by smaller, lighter air particles travelling at high speeds. Which is why smoke particles are observed to move randomly. This is also evidence to the fact than air is made up of tiny atoms moving really quickly.

Question 34

How is pressure produced in a container?

Answer 34

Gas particles collide with the inside of the container The collision is assumed to be elastic so, Ek is conserved. The change in momentum is -2mv Creating a force of -2mv/t

Question 35

Explain what happens to pressure as temperature is increased.

Answer 35

Particles have a higher speed and more momentum. Change in momentum is higher during collisions So, force exerted is higher. The frequency of collisions with the wall also increases.

Question 36

Explain what happens to pressure as volume increases.

Answer 36

The particles travel further between collisions with the wall. So, frequency of collisions decreases. So, rate of change of momentum decreases, decreasing force. So, pressure will decrease.

Question 37

What are the assumptions of the kinetic theory of an ideal gas?

Answer 37

Particles move with rapid, random motion Collisions are elastic Atoms have negligible volume There are no intermolecular forces, all internal energy is Ek. Collisions time is negligible

Question 38

What is Boyle’s law?

Answer 38

The pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature of the gas is constant. pV = constant

Question 39

What is Charles law?

Answer 39

At a constant pressure and for a fixed mass of gas, the volume of gas is proportional to the absolute temperature. V / T = constant

Question 40

What is the pressure law?

Answer 40

For a fixed mass of gas at a constant volume, the pressure is directly proportional to the absolute temperature. p / T = constant

Question 41

What is the equation which combines Boyle’s, Charles and the pressure law?

Answer 41

p V / T = constant