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What does it mean if a collision is elastic?
Both linear momentum and kinetic energy are conserved.
What does it mean if a collision is inelastic?
Linear momentum is conserved however kinetic energy is not. Kinetic energy is transferred to other types of energy forms.
How is resultant force linked to momentum?
Force is equal to the rate of change of momentum.
What is impulse? How is it linked to a Force-Time graph?
- Impulse is equal to the change of momentum of an object.
- It is the area of the graph.
In SHM, what is the phase difference between the displacement, velocity and acceleration?
The velocity is pi/4 ahead of displacement and acceleration is pi/4 ahead of velocity. This makes displacement and acceleration out of phase with eachother.
In SHM, at what point does the object have the highest potential energy? The highest kinetic energy?
- The maximum potential energy is when the object is at maximum amplitude.
- The maximum kinetic energy is when the object is at the equilibrium position.
What is a free vibration?
- Free vibrations involve no transfer of energy to or from the surroundings. The object will oscillate at it's natural frequency.
- In theory this means the object will oscillate at the same amplitude forever. In practice this never happens so vibrations in air are called free vibrations aswell.
What is a forced vibration?
Forced vibrations happen when there is an external driving force applied periodically. The frequency of this force is called the driving frequency.
What is phase difference between an object and it's driving force when...
the driving frequency is below natural frequency?
the driving frequency is natural frequency?
The driving frequency is above natural frequency?
- The object and driving force are in-phase.
- The object and driving force have pi/4 phase difference.
- The object and driving force are out of phase.
What is resonance?
When a driving force reaches an objects natural frequency, amplitude is greatly increased as it receives more energy from the driving force. The phase difference between driver and driven is pi/4 in this case.
What is damping? How can damping be useful?
- Damping is reducing the amplitude of an oscillation until it becomes zero. Damping can either be deliberate or due to frictional forces.
- Damping is useful in car suspension and closing heavy doors slowly.
Name four types of damping. How are they different?
- Light, heavy, overdamping and critical.
- If lightly damped, a system takes a long time for it to stop oscillation and only loses a small bit of amplitude each period.
- If heavily damped, a system takes less time to stop and amplitude gets much smaller each period.
- If overdamped, a system does not oscillate but it takes a long time for it to come to rest.
- If critically damped, amplitude is reduced in the shortest time possible so no oscillations occur.
In a gravitational field diagram, what does the direction of the field lines represent? What about an electrical field?
- The direction on a g field represents the direction a mass would move when within the field.
- For an e field, the direction represents the direction a positive charge would move.
What is gravitational potential?
Is the amount of energy required to move a point mass from infinity to a point within a gravitational field. Therefore, all gravitational potential values are negative (apart from infinity=0) as energy is released when falling into a g field.
What is the equation for the time period of a satellite?
- This can be derived using the formula book but it will be easier to remember this.
What are geosynchronous and polar orbits?
- Geosynchronous satellites have an orbital period of 24 hours. This means they should always be above the same point on the earth continuously. Useful for communications.
- Polar orbits go over both poles of the earth. This allows them to be above every bit of the earth at some point or another. Useful for spying satellites.
How does the kinetic and potential energy of a satellite change throughout a circular orbit? What about an elliptical orbit?
- In a circular orbit, as the distance between the earth and satellite doesn't change and total energy is constant, KE and PE doesn't change.
- In an elliptical orbit, the distance between earth and the satellite changes constantly. As the satellite approaches the earth, it will gain KE and lose PE and vice versa when travelling away from it.
What is electric field strength defined as?
The force per unit positive charge. (NC-1)
What is electrical potential?
It is the amount of energy required to move a unit positive charge from infinity to that point. So if the charge creating the field is positive, the potential would be positive as energy is required to overcome repulsive forces. Vice versa if charge creating the field is negative.
What are some similarities between gravitational fields and electric fields?
Apart from the different constants used in equations, what is a difference between them?
- They both are affected by the inverse square law (F is proportional to r-2)
- G field strength is force per mass whereas E field strength is force per unit positive charge.
- They both have zero potential at an infinity distance away from the field.
- Radial and uniform fields are drawn and in the same way.
- They are different as G fields are only ever attractive and E fields can be either attractive or repulsive.
What is capacitance?
It is the amount of charge an object can store per unit potential difference across it. (Measured in farads or CV-1)
How does a capacitor work?
A capacitor is made of two electrically conductive plates with an insulator between them. This means that, when connected to a D.C. supply, the one plate becomes negatively charged and the other becomes positively charged but the insulator prevents movement of charge between the plates. This means a p.d. builds up between the plates.
What is the time constant? Use a definition and an equation.
- The time taken for a discharging capacitor to fall to 37% of total charge or for a charging capacitor to reach 63% of total charge.
- t = RC
When a capacitor is charging how does the circuit's current, p.d. across capacitor and charge across capacitor change with time?
When charging, current follows an exponential decay curve as less and less current flows as the capacitor gets closer to being fully charged. For p.d. and charge, the curve follows an inverse exponential curve. The capacitor charges a lot to begin with but, as the capacitor starts to resist the current, it gets harder and harder to charge to full capacity meaning less p.d. and charge is added per second.
When a capacitor is discharging how does the circuit's current, p.d. across capacitor and charge across capacitor change with time? Why?
All three follow an exponential decay curve. As a complete circuit (without battery) is connected, the current in the circuit starts flowing very quickly because the p.d. between the negative plate and positive is also high. As electrons continue to flow from negative to positive plates, the electric potential of the plates gets more equal so p.d. approaches zero. As p.d. approaches zero, so does current and charge.
What is the difference between Fleming's left and right hand rules?
- The left hand rule is used for motors as the magnetic field and current produce a force whereas the right hand rule is used for generators as a current is induced.
- Remember, the finger for current shows the direction of conventional current, so positive to negative.