Oscillations - A level Physics Edexcel

What is an oscillation?

Repetitive motion about a fixed point

What are the conditions in a pendulum when x=A?

At rest momentarily, KE=0, V=0, maximum force and acceleration as maximum component of tension horizontally, max GPE

What are the conditions in a pendulum when x=0?

Equilibrium, min GPE, max KE, Vmax, constant velocity, zero resultant force (T=W)

Where does the restoring force act?

Towards the centre of the oscillation

What is the first condition for SHM?

The resultant force (and therefore its acceleration) acting on the body is directly proportional to the displacement from a fixed point (the distance from the equilibrium position).

What is the second condition for SHM?

The resultant force (and acceleration) act towards the equilibrium position.

How can the movement of an oscillator be shown?

By plotting its displacement from the origin x against time t.

What is the equation for the time period for a SHM spring (independent of extension)?

T= 2 pi root m/k

What is the equation for the time period for a SHM pendulum (independent of bob mass and displacement)?

T= 2 pi root l/g

Which equation gives the maximum acceleration?

a= w^2A

What always acts in the same direction in SHM?

Velocity and acceleration

What in SHM always acts in the opposite direction?

Acceleration and displacement

What is the gradient of the displacement time graph?

The velocity of an oscillating object

What type of energy is all the energy of a pendulum it its highest?

Gravitation potential energy

What is GPE converted to as a pendulum falls?

Kinetic energy (KE)

When does the potential energy in a pendulum stop being converted to kinetic energy?

When the mass is at the equilbrium position where the net force on the mass is zero. Potential energy is now zero.

Total energy=

Kinetic energy + potential energy

How do you find the SHM total energy?

The total energy must be same as the maximum kinetic energy

When does damping occur?

When resistance is added to the motion of an oscillator.

Why will a mass on a spring eventually stop oscillating?

Most oscillators are damped

What happens if something is underdamped?

The system oscillates before coming to a stop

What does critically damped mean?

The smallest amount of damping required for a system to not oscillate.

What does overdamped mean?

Any more damping than critically damped.

How do you damp something?

By increasing air resistance by increasing surface area or increasing viscosity of fluid it is travelling through (swap air for liquid)

What is a free oscillator?

An oscillator that is set into motion and has no periodic force acting on it

What are some examples of free oscillating systems?

Masses on springs and pendulums

What is a forced oscillation?

One for which a periodic force acts on the oscillator, affecting its oscillation.

What does a free vibration oscillate with?

A natural frequency

What is resonance?

When the driving force applied with a natural frequency oscillates at the natural frequency so the amplitude is a maximum

When will the motion of a spring be harmonic?

If the spring obeys Hooke's law

What are some examples of SHM?

A car bouncing on its suspension system, a person bouncing on the end of a bungee cord and a swinging pendulum in a grandfather clock.

Why is a child jumping on a trampoline not SHM?

The restoring force isn't proportional to the extension

Describe how you would use data from the graphs of h and a against t to check that the motion of the mass was simple harmonic

Read off h value and use it to get displacement, calculate ratio eg a/x, check ratios to see if constant - the constant will be negative if SHM

What is natural frequency?

The frequency at which a body oscillates in the absence of a driving force.

How do you reduce the risk of the bob in the pendulum experiment?

Use of a G-clamp, limit bob mass and small displacements.

What is the damping force acting on an oscillating always?

In the opposite direction to the velocity

State what is meant by simple harmonic motion

When the resultant force acting on the oscillating body is directly proportional to the displacement from the equilibrium position and the resultant force always acts towards the equilibrium position.

What would be the most important property of a material used in a mechanism to transfer kinetic energy from the ground in an earthquake to a building?

Ductility

Hollow spaces built into a tennis racket frame and small lead spheres are packed into these spheres. Explain how this dampens the oscillation.

Spheres collide hence energy dissipated so the amplitude of oscillations decrease with time as shown by the graph

Why is there a minus sign in F=-Kx?

Force is in opposite direction to the displacement from the equilibrium position

Explain what is meant by damping in a mass spring system and why damping is desirable in a mass spring system in a building

Providing resistance to the motion of the masses of the energy is transferred to the dampener from the mass spring system and dissipated in the surroundings so the amplitude of oscillation is reduced

What is meant by resonance on a bridge?

Resonance occurs when the bridge is forced into oscillation at its natural frequency. This means that the amplitude of the oscillation of the bridge is very large which may damage the bridge.

Describe how the behaviour of the fluid in a dampener changes in a magnetic field and how this would be useful for the operation of the dampeners

The more viscous the fluid, the more resistance there would be to motion through it and a greater resistance to movement would result in and greater energy dissipation