Mock Revision - ignore Flashcards
Speed and Stopping Distances
Speed ∝ Thinking Distance
Speed^2 ∝ Braking Distance
Upthrust
The upwards force that a fluid exerts on a body floating in it due to the fluid displaced
Factors Affecting Drag
- Velocity (drag ∝ velocity^2)
- Cross sectional area of the object
- Density of the fluid
The more of the object submerged
The greater the upthrust
To travel further
Streamline
Stiffness
The ability of a material to resist a tensile force
Extension depends on
- material
- length
- cross sectional area
Ductile
Material can be drawn into wires
Malleable
Material can be hammered into flat sheets
Hard
Material will resist plastic deformation by surface indentation or scratching
A Newton’s Third Law pair of forces must
- be the same type of force
- act in opposite directions
- act on different objects
Impulse =
Change in momentum
Energy Flows
Hotter –> Cooler
Thermal Equlibrium
Two objects in contact with each other at the same temperature are said to be in thermal equilibrium
Min internal energy at
absolute zero: no kinetic, some potential
Kinetic Model of Matter (general + s,l,g)
In kinetic model of matter, all matter is made up of very small particles which are in constant motion
- Solids: vibrate about their fixed positions
- Liquids: slide past one another
- Gases: free to move quickly in random directions
Internal Energy
The sum of the randomly distributed kinetic and potential energies of all the atoms/molecules within a system
In system of gas particles at fixed temp
There is a distributed of kinetic energies among the molecules
- since wide range of different translational speeds
- peak of curve = most probable speed
Brownian Motion
The random movement of small visible particles suspended in a fluid due to collisions with much smaller, randomly moving atoms/molecules of the fluid
Brownian Motion: as visible particle mass increases
Velocity decreases, so they move around less
Specific Heat Capacity
The energy needed to increase the temperature of 1kg of a substance by 1K
Specific Latent Heat of Fusion/Vaporisation
The energy needed to melt/boil 1kg of a substance
An Ideal Gas
A gas that has internal energy only in the form of random kinetic energies
Real gases behave like ideal gases if
- The temperature is well above its boiling point
- The pressure is low so that the particles are far apart
Assumptions of the kinetic model of gas
- The gas contains a large number of particles
- The particles move rapidly and randomly
- All collisions are perfectly elastic
- There are negligible attractive forces between particles except during collisions
- The time for a collisions to happen is negligible compared to the time between collisions
- Particles have a negligible volume compared with the volume of gas in the container
Boyle’s Law
p ∝ 1/V
- where T constant
- where number of moles is constant
Charles’s Law
V ∝ T
- where p constant
- where number of moles is constant
Pressure Temperature Law
p ∝ T
- where V is constant
- where number of moles is constant
Ideal Gas Proportionality
T ∝ Ek for ideal gases since they have negligible potential energy
All gases at the same temperature have the same Ek
Internal Energy of a ideal gas
3/2 NkT
Circular Motion: Time Period
The time taken for one complete circular path
Linear Velocity
The velocity at a given time
Angular Velocity
The rate of angular rotation
Acceleration is proportional to
Linear Velocity
Centripetal Acceleration Acts
- inwards towards the centre
- perpendicular to linear velocity
Centripetal Force
The resultant force on an object acting towards the centre of the circle causing it to move in a circular path
Centripetal Force is the resultant of
Tension and Weight
Vertical Circle: slowest at
- the top (centripetal force = weight)
- if weight > centripetal force, won’t spin in vertical circle
- acceleration > 9.81
Simple Harmonic Motion
A body will oscillate with S.H.M if its acceleration is directly proportional to its displacement from a fixed point and always directed towards that fixed point (a ∝ -x)
In SHM
amplitude and time period is constant
Damping
Damping forces reduce the amplitude of an oscillation with time due to energy being removed from the system
Resonance
- When driving frequency = natural frequency of the system
- Results in body oscillating with a max amplitude due to max energy transfer
As damping forces increase
- The rate of energy removal from system increases
- The period will increase slightly
A Gravitational Field
The region around a body in which other bodies will feel a force due to the mass of the body
Gravitational field strength is
- Uniform over short distances
- At 2x distance, field has 1/4 strength (inverse square law)
Geostationary Satellites
- Same place above surface at all time
- 24 hour time period
- Monitoring the weather, broadcasting TV signals
Gravitational Potential
- Grav potential at a point in a gravitational field is the energy required per unit mass to move an object from infinity to that point in the field
- Vg is defined to be 0 at infinity
Gravitational Potential Energy
Grav potential energy = work in bringing an object from infinity to a point in the field
Escape Velocity
- The escape velocity from a point in a gravitational field is the minimum launch velocity required to move an object from that point to infinity
- ½ mv2 ≥ GMm/r
