3.6 Further mechanics and thermal physics Flashcards
What are the requirements for an object to move in circular motion at a constant speed?
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)
Which factors affect the centripetal force?
↑ Mass of the object → ↑ Centripetal force
↑ Speed of the object → ↑ Centripetal force
↑ Radius → ↓ Centripetal force
How do you calculate angular speed?
(Velocity) / (radius)
2(pi)f
Only works for radians
How do you calculate centripetal acceleration?
(m*v^2)/r
m * ω ^2 * r
What are the 2 conditions required for SHM?
The acceleration of a body is proportional to its displacement from the equilibrium position.
The acceleration acts towards equilibrium position.
What is the equation for acceleration in SHM?
a = - ω^2 * x
What is the equation for displacement in SHM?
x = A * cos(ωt)
Displacement = (amplitude ) * cos[(2 pi * frequency)(time)]
What is the equation for velocity in SHM?
v = 土 ω * sqrt [A ^2 - x ^2]
What are the 2 main examples of simple harmonic motion?
Pendulums
Mass on a spring
What is the equation for maximum speed in SHM?
v = ωA
Velocity = (2pi * frequency) * (acceleration)
What is the equation for maximum acceleration in SHM?
a = ω^2 * A
Acceleration = (2pi * frequency)^2 * (acceleration)
Which factors affect the period of a pendulum?
The length of the string
What happens when a system is under damped?
The system oscillates before coming to a stop.
What happens when a system is critically damped?
This is the smallest amount of damping required for a system not to oscillate.
What is over damping?
More damping than critically damped.
What is free oscillation?
There’s no forces acting other than internal forces
There’s no energy transfer
What is forced oscillation?
The oscillator is acted on by a periodic external force
There’s periodic energy transfer
What is resonance?
It occurs when driving frequency = natural frequency
The amplitude of vibration increases to maximum leading to maximum energy transfer.
What is the definition of internal energy?
The sum of the randomly distributed kinetic energies and potential energies of the particles in a body.
How do you increase the internal energy of a system?
When energy is transferred to it by heating or work is done on it.
What happens to internal energy when state is changing?
The potential energies of the particles are changing but not the kinetic energies.
How can you tell when potential energy has increased?
The distance between the particles will increase.
How can you tell when average Ek of the particles has increased?
The temperature of the substance will increase.
Describe the internal energy of a solid.
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.
Describe the internal energy of a liquid.
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.
Describe the internal energy of a gas.
Has the highest Ek as it has the highest temperature.
Largest Ep as the molecules are free from each other and very far apart.
What is the specific latent heat of fusion?
The thermal energy released when a liquid changes into a solid, at a constant temperature, per unit mass.
What is the specific latent heat of vaporisation?
The thermal energy required to change a liquid into a gas, at a constant temperature, per unit mass.
What is specific heat capacity?
The amount of energy required to raise the temperature of a unit mass of a substance by unit temperature.
Which is worse, a scald from steam or water, both at 100 C?
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.
What is thermal equilibrium?
For bodies at the same temperature, there’s no net flow of thermal energy.
What is brownian motion?
Random motion is a result of collisions with fast, randomly-moving particles in the fluid.
What is the evidence for Brownian motion?
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.
How is pressure produced in a container?
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
Explain what happens to pressure as temperature is increased.
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.
Explain what happens to pressure as volume increases.
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.
What are the assumptions of the kinetic theory of an ideal gas?
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
What is Boyle’s law?
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
What is Charles law?
At a constant pressure and for a fixed mass of gas, the volume of gas is proportional to the absolute temperature.
V / T = constant
What is the pressure law?
For a fixed mass of gas at a constant volume, the pressure is directly proportional to the absolute temperature.
p / T = constant
What is the equation which combines Boyle’s, Charles and the pressure law?
p V / T = constant
