p10 - forces and motion Flashcards
define momentum
- a property of any moving object
- calculated as product of mass and velocity
- measured in kg m/s
define a system
- systems are how physicists divide up the universe
- involve objects interacting
- anything from a falling object to our whole galaxy
define a closed system
- system where objects are not affected by external forces or other objects outside system
- momentum and energy are conserved in a closed system
define conservation
- ‘keeping the same’
- total amount of a quantity is the same before and after an event
- in any closed system, the total amount of energy and momentum before and after an event is equal
give the equation for momentum
p = m v
momentum (kg m/s) = mass (kg) x velocity (m/s)
define newtons second law of motion
acceleration is
- proportional to resultant force of an object
- inversely proportional to the mass of the object
define inertia
tendency to stay at rest or in uniform motion
what happens when the force acting on an object is its weight?
the equation F = m a becomes W = m g (weight N= mass (kg) x acceleration to to gravity (m/s²)
define terminal velocity
- resultant force at 0
- object stops accelerating
- moves at constant velocity
explain motion of object falling in a fluid in terms of forces
- fluid exerts a drag force on object, resisting its motion
- faster the object falls, the bigger the drag force becomes
- eventually it will become equal
define stopping distance
thinking distance (distance vehicle travels during driver’s reaction time) + braking distance (distance it travels under braking force
how can braking distance be increased?
- poorly maintained roads
- bad weather conditions
- poorly maintained vehicles
how can deceleration be calculated?
rearrange
v² = u² + 2as for s or a
how is momentum conserved?
collision or explosion as no external forces act on the objects
define an elastic object
one that regains shape when forces changing it are removed
