Further Mechanics Flashcards
What is Newton’s 1st law?
When there is no overall resultant force acting on an object, it will either remain stationary or move at a constant velocity
What is Newton’s 2nd law?
There is a proportional relationship between the resultant force and acceleration, shown by ΣF = ma
What is Newton’s 3rd law?
For every force A exerts on B, B exerts an equal and opposite force on A
Show how force can be thought of as rate of change of momentum
F = ma a = (v-u)/t F = (mv - mu)/t = Δp/Δt
What is the principle of conservation of momentum?
Within a closed system, the total momentum in any direction is the same before and after a collision
What is an elastic collision?
A collision where KE is conserved
What is an inelastic collision?
A collision where KE is not conserved
How would a jet engine provide a forward thrust? (With reference to Newton’s laws)
- The jet engine burns fuel and ejects hot gas at high speed out the back of the engine
- The engine provides a force on the gas particles
- Newton’s 3rd law: equal and opposite reaction force of the gas particles on the engine and therefore the plane
- Newton’s 1st law: unbalanced force gives it an acceleration
What is impulse?
The force multiplied by the time over which it acts
What is a non-relativistic particle?
A particle travelling at a speed lower than the speed of light, so the mass stays constant
What is the definition of a radian?
The angle subtended at the centre of the circle by an arc of length equal to the circle’s radius
What is meant by centripetal acceleration?
The direction of velocity is constantly changing so we say the object is accelerating. An unbalanced force (weight or tension) provides an acceleration (F = ma, Newton’s 1st law). The acceleration is always directed towards the centre of the circle
In a vertical circle, where is tension highest?
At the bottom, where weight acts against centripetal force
What provides the centripetal force for a satellite orbiting the Earth?
The gravitational force of the Earth pulling the satellite/its weight
What provides the centripetal force for an electron in a hydrogen atom?
The electrostatic attractive force of the positively charged nucleus
What provides the centripetal force for a car cornering on a banked road?
The horizontal component of the reaction force of the car on the road
What provides the centripetal force for an air craft banking?
The horizontal component of the lift force
Practical to investigate the relationship between radius and velocity for a spinning bung
- Attach a bung to a string threaded through a plastic tube with a mass hanger with 100g hanging off the end
- Mark the string every 10cm at the point where it comes out of the tube
- Keep the 0.1m mark in line with the bottom of the tube and spin it around, measuring the time taken for 50 complete orbits
- Calculate the time taken for 1 orbit, then calculate velocity (2πR/T)
- Repeat this until R=60cm
- Plot a graph of v² against R and calculate gradient (F/m)
- Calculate the mass of the bung (v² = FR/m)
- Measure the mass of the bung and calculate % difference
What are 2 limitations of the spinning bung practical?
- Human error with timing - minimise this by repeating more times and taking an average
- Friction increases value of calculated force - reduce by using a different material or lubricant
For the conical pendulum, what provides the centripetal force?
The horizontal component of tension
For the conical pendulum, what keeps the bung in a horizontal circle?
Vertical component of tension is balanced by weight, so it remains horizontal
For the conical pendulum, why does tension increase as the speed increases?
At greater speeds, tension increases because greater centripetal force needed at higher speed (mv²/r)
At larger values of θ, vertical component is a smaller proportion of tension but is always still equal to mg (mg = Tcosθ - if θ is larger, T must be larger)
If the lift force of a plane remains constant, what else will happen to the plane as it starts to turn in a banked circle?
Plane will start to lose altitude - size of vertical component will decrease so it no longer balances mg
How can artificial gravity be created?
Spinning something so that centripetal acceleration is equal to g
Why do you feel weightless when a plane spins in a circle, for example?
At the top of a loop, centripetal force provides weight, but there is no reaction force, so pilot would feel weightless
Generally, it is when the reaction force is zero/at the point of being zero that you feel weightless, as it is reaction force pushing against a person which makes you feel you have a weight
What is the expression for centripetal force at the top and bottom of a vertical loop?
Ftop = W - Rt Fbottom = Rb - W
