p2 - forces

Cards (49)

  • equation linking speed, distance and time
    distance (m) = speed (m/s) x time (s)
  • how can speed be calculated fro a distance-time graph?
    the speed is equal to the gradient of the graph
  • what must be done to calculate speed at a given time from a distance-time graph for an accelerating object?
    • drawing a tangent to the curve at the required time
    • calculating the gradient of the tangent
  • equation for acceleration
    acceleration (m/s^2) = change in velocity (m/s) / time taken (s)
  • how can distance travelled by an object be calculated from a velocity-time graph?
    it is equal to the area under the graph
  • what is a scalar quantity?
    a quantity with only magnitude and no direction
  • what is a vector quantity?
    a quantity with both magnitude and direction
  • how can a vector quantity be drawn and what does this show?
    • as an arrow
    • the length of the arrow represents the magnitude
    • the arrow points in the associated direction
  • examples of vector quantities
    • force
    • displacement
    • velocity
  • examples of scalar quantities
    • temperature
    • time
    • mass
    • speed
    • distance
  • how do you calculate average speed for non-uniform motion?

    average speed (m/s) = change in distance (m) / change in time (s)
  • what piece of apparatus may be used to record the time taken for a very fast object to move a given distance?
    light gates
  • what is a force?
    a push or pull acting on an object due to an interaction with another object
  • two categories force can be split into:
    1. contact force (objects touching)
    2. non-contact force (objects separated)
  • examples of contact force
    • friction
    • air resistance
    • tension
  • examples of non-contact force
    • gravity
    • electrostaticity
    • magnetism
  • what is the name given to the single force that is equivalent to all the other forces acting on a given object?
    resultant force
  • newton's first lawon a stationary object
    if the resultant force on a stationary object is zero, the object will remain at rest
  • newton's first law on a moving object
    if the resultant force on a moving object is zero, the object will remain at constant velocity
  • if an object changes direction but remains at a constant speed, is there a resultant force?
    since there is a change in direction, it means there is a change in velocity so there must be a resultant force
  • when does an object fall with terminal speed?
    • when the upwards forces (air resistance) and the downwards forces (weight) are equal to each other
    • no resultant force, so constant speed
  • what happens to the magnitude of air resistance on a falling object when the velocity increases?
    as velocity increases, the force of air resistance on the object will also increase
  • equation for newton's second law
    • resultant force (N) = mass (kg) x acceleration (m/s^2)
    • F = m x a
  • newton's second law
    an object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass
  • what is inertia?
    • the tendency of an object to continue in its state of rest or uniform motion
    • an object's resistance to motion
  • what is intertial mass?
    • a measure of how difficult it is to change a given object's velocity
    • the ratio of force over acceleration
  • newton's third law
    whenever two objects interact, the forces that they exert on each other are always equal and opposite
  • equation used to calculate an object's momentum
    momentum (kg m/s) = mass (kg) x velocity (m/s)
    P = m x v
  • unit used for momentum
    • kg m/s
    • kilogram metres per second
  • in a closed system, what can be said about the momentum before and after a collision?
    the total momentum before is equal to the total momentum afterwards
  • equation linking change in momentum, force and time
    • force x time = change in momentum
    • F x Δt = P
    • F x Δt = m x Δv
  • explain how a seatbelt improves a passenger’s safety during a collision
    • the passenger must decelerate from the vehicle’s velocity at impact to zero, so they experience a force.
    • this force is equal to the rate of change of momentum.
    • seatbelts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force felt by the passenger
  • what quantity is equal to the force experienced in a collision?
    the rate of change of momentum
  • what does it mean if a force is said to have done 'work'?
    the force causes an object to be displaced through a distance
  • what is the equation used to calculate work done? give appropriate units.
    • work done (J) = force (N) x distance (m)
    • W = F x d
  • under what circumstances is one joule of work done?
    when a force of one newton causes a displacement of one metre
  • what is power?
    the rate of which work is done
  • unit for power
    watt (W)
  • what is one watt equal to?
    • one joule per second
    • 1 W = 1 J/s
  • equation used to calculate power
    power (W) = work done (J) / time (s)