SP2 - Motion and Forces ✓ Flashcards Preview

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Flashcards in SP2 - Motion and Forces ✓ Deck (24)
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SP2a - If a rocket experiences 800kN of thrust upwards and its weight is 300kN, what is the resultant force?

800 is up 300 is down.

800 - 300 = 500

500kN upwards


SP2b - What is Newton's first law?

  • A moving object will remain at a constant velocity until an external force acts on it.
  • A stationary object will remain stationary until n external force acts on it.


SP2b - What is centripetal force?

  • An object moving in a circle at a constant speed is contantly changing velocity and so is constantly accelerating towards the centre of the circle.
  • As the car is accelerating, there must be a force acting on it.
  • This is centriputal force and always acts towards the centre of the circular motion.


SP2b - What three things can provide centriputal force?

  • Tension
  • Friction
  • Gravity


SP2b - How can the amount of centripetal force needed for an object to remain in circular motion be altered?

The amount of force needed increases if you:

  • Increase the mass of the object
  • Increase the speed of the object
  • Decrease the radius of the circle


SP2c - What is the difference between weight and mass?

Mass is the quantity of matter in an object and weight is the pull force the object experience depending on the gravitational field strength.

Weight - N

Mass - Kg


SP2c - What formula links weight and mass?

w = m x g

(Weight = mass x gravitational field strength)


SP2c - Describe the forces acting on a skydiver as they jump out of a plane?

  • As soon as they jump out, the only force acting on them is their weight and so they accelerate downwards
  • Air resistance increases with speed and so as they accelerate, it increases until eventually it is equal to their weight
  • At this point the resultant force acting on the skydiver is 0 and so they stop changing velocity as they have reached terminal velocity
  • Once the parachute is launched, the air resistance greatly increases causing a decceleration
  • As the velocity decreases so does the air resistance until it is again equal to the weight
  • It now reaches a new lower terminal velocity


SP2d - What is Newton's second law of motion?

The acceleration of an object depends on:

  • Its mass
  • The Force acting on it


SP2d - What equation uses Newton's second law?

F = m x a

(Force = mass x acceleration)


SP2d - What is inertial mass?

  • A measure of how difficult it is to accelerate an object.
  • The ratio of the force needed to accelerate an object over the acceleration produced.
  • If an object has a lerger inertial mass, it will require more force to produce a given acceleration than an object with a larger inertial mass.


SP2d CP - How can you investigate the acceleration of a trolley using light gates?

  • Attach masses to the end of the trolley hanging off the end of the table over the ramp and the pulley .
  • Set up two light gatesa measured distance apart.
  • Connect the light gates to a data logger.
  • Release that masses. using your data log information, divide the length of the card by the time the light gate was active for each of the light gates.
  • Divide the difference between these two velocities by the time between each of them to get the acceleration.
  • To investigate how mass affects this, repeat with different masses.


SP2e - What is Newtons third law?

When objects interact the forces exerted are equal and opposite.


SP2e - When a person is standing, describe the action-reaction forces.

The downward force of weight from the person on the ground and the upward reaction force of the ground on the person.


SP2e - What is the difference between balanced forces and action-reaction forces?

Balanced forces all act on the same object, action-reaction forces act on different objects.


SP2f - What is the formula for momentum?

p = m x v

(momentum [kg m/s] = mass x velocity)


SP2f - What equation connects force and momentum, and how can this be derived?

F = Δp / t

(Force = change in momentum ÷ time)

As F = m x a

and a = Δv / t

we can see that

F = (m x Δv) ÷ t

Since m x v = p

then m x Δv = Δp

So, F = Δp ÷ t


SP2f - What is the law of the conservation of momentum, and how id this affected by the fact that momentum is a vector quantity?

  • Total momentum before = total momentum after
  • Since momentum is vector, an object moving in the opposite direction has a negative momentum and this must be taken into account when calculating momentum.


SP2g - What is stopping distance?

  • The total distance it takes for a car to stop once the driver reacts to an external stimuli.
  • This consists of: Thinking distance & braking distance


SP2g - What is the average reaction time to visual stimuli and what can affect this?

  • 0.25 seconds.
  • This can be longer if the driver has taken drugs/ alcohol or hasn't had enough sleep


SP2g - What can increase the braking distance of a car?

  • Increasing its momentum:
    • If it is moving faster
    • Higher mass
  • Reducing friction:
    • Brakes are worn
    • Rain/ice/snow on the roads
    • Loose gravel


SP2h - How can you combine the formulae for work done and KE to have a formula for braking distance?

E = F x d

KE = 1/2 x m x v²

(1/2 x m x v²) ÷ F = d

d = (m x v2) ÷ 2F

Mass x velocity² divded by 2 force = braking distance

[Also can be (p x v) ÷ 2F = d Momentum x velocity ÷ 2 Force = Braking distance]


SP2i - What are the four main safety features of a car?

  • Air bags
  • Crumple zones and side impact bars (Easily give way causing themsleves to crush)
  • Seat belts


SP2i - Explain how the safety features of a car link to the equation linking force and momentum.

  • F = Δp / t
  • All the safety features of a car absorbe kinetic energy, increasing the time taken for the momentum to reduce.
  • As the time is increased, the force is reduced.