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state the symbol equation to find momentum
p (kgm/s) = m (kg) x v (m/s)
state what happens to momentum in a closed system
the total momentum before an event
is equal to the total momentum after the event
therefore energy is conserved
state an example of momentum in an event
collision
state what elastic collision is
when objects collide
and move in opposite directions
state what inelastic collision is
when objects collide
and move in the same direction
state what happens to kinetic energy in an elastic collision
kinetic energy is conserved
state what happens to kinetic energy in an inelastic collision
kinetic energy is not conserved
and it is wasted as heat energy
state what happens to mass and velocity of multiple objects in an elastic collison
the mass and velocity combine
state what happens to momentum in a collision
momentum is always conserved in a collision
explain how to complete calculations of a collision
write down the known mass and/or velocity of both objects
use these to calculate the momentum of one of the objects
the momentum will be the same before and after the event
use the equation p = m x v to find any unknown data
state what causes a change in momentum
when a force acts on an object that is moving
or able to move
state the symbol equation to find force using mass and acceleration
F (N) = m (kg) x a (m/s²)
state the symbol equation to find acceleration
a (m/s²) = Δv (m/s) / t (s)
state the equation to find force using acceleration, mass and time
F (N) = (m (kg) x Δv (m/s)) / t (s)
state the definition of force
rate of change of momentum
explain how air bags/seat belts work as safety features
air bags/seat belts absorb energy from collision by changing shape
for a given force upon impact, the air bags/seat belts absorb energy
and increase the time over which the force takes place
this increases the time taken for the change in momentum of the passenger and the vehicle to come to rest
the increased time reduces the force and thus the risk of injury to the passenger
explain why air bags are useful as safety features
they act as a soft cushion to prevent injury on the passenger
when they are thrown forward upon impact
explain why seat belts are useful safety features
they are designed to stop a passenger from colliding with the interior of a vehicle
by keeping them fixed to their seat in an abrupt stop
they are designed to stretch slightly
to increase the time for the passenger’s momentum to reach zero
and therefore reduce the force of the collision on the passenger
explain how gymnasium crash mats work as safety features
when an object lands on the crash mat with a large force
the soft landing means the object is in contact with the mat for a longer period of time
than if the mat was not there
this increases the contact time over which their momentum is reduced
creating a smaller impact force and a lower chance of injury
explain how cycle helmets work as safety features
when a cyclist’s helmet collides with a surface
the foam inside the helmet compresses upon impact
absorbing some of the energy during collision
slowing down the rate of change of momentum
this reduction in the rate of change of momentum leads to a decrease in the force experienced by the cyclist’s head
thus providing protection in case of collision
explain how cushioned areas in playgrounds work as safety features
when a child falls in the playground
the cushioned surface reduces the risk of severe injury by increasing the contact time of the child
the mat will be thinner than crash mats as children have a lower mass than adults
explain how increasing contact time in a collision protects passengers
causes rate of change of momentum to decrease
causes passenger to experience a smaller force
decreasing risk of injury
explain how increasing contact time in a plane landing is more comfortable for passengers
rate of change of momentum is slower
decreases force experienced by passengers
explain why some planes need longer runways to land safely
some planes have a larger mass
causing the aircraft to have more kinetic energy
due to it having more momentum
state what a scalar quantity is
quantity with magnitude
state what a vector quantity is
quantity with magnitude and direction
state the definition of a force
the rate of change of momentum
state the definition of a contact force
when a force is exerted when objects are physically-touching
state the definition of a non-contact force
when a force is exerted when objects are physically-separated
state examples of contact forces
friction
air resistance
tension
normal contact force
state examples of non-contact forces
gravitational force
electrostatic force
magnetic force
state what kind of quantity force is
vector
state what kind of force weight is
force acting on an object
due to gravity
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Flashcard (187)