P10 Force and Motion Flashcards
What is Newton’s Second Law of Motion?
the acceleration of an object is:
- PROPORTIONAL to its DIRECTION,
- INVERSELY PROPORTIONAL to the MASS of the object.
what is inertia?
the tendency of an object to stay at rest or continue in uniform motion
what is the resultant force on an object falling in fluid?
its weight minus the frictional force on it
why does the acceleration of an object decrease as it falls?
because frictional force on the object increases
as it speeds up
what is terminal velocity?
when the frictional force on an object is equal and opposite to its weight
resulting in constant velocity
the braking force needed to stop a moving vehicle from a fixed distance depends on:
- the speed it moves at,
- its mass.
define stopping distance
the shortest distance a vehicle can safely stop in
stopping distance formula
THINKING DISTANCE + BRAKING DISTANCE = STOPPING DISTANCE
factors affecting braking distances
- adverse road conditions (which increase braking distance to avoid slipping),
- drugs, alcohol, distraction (which increase thinking distance)
- faster vehicle (increases thinking and braking distance)
- poorly maintained vehicles (less effective tyres/brakes increase braking distance)
dangers of large decelerations
- brakes overheat,
- loss of control over vehicle.
what is momentum?
momentum (kg m/s) = mass (kg) x velocity (m/s)
what is the law of conservation of momentum?
the total momentum before and after an event in a closed system is equal
what is the momentum of an object at rest?
0
because its velocity is 0
how do crumple zones reduce the force of an impact?
increase impact time
reducing the change of momentum per second
decreasing force of impact
(reduce momentum at front, increase at back)
what is impact force?
change of momentum per second
describe the forces that two vehicles would each exert onto each other during a collision
in which no external forces act
exert equal and opposite forces onto each other
creating a total momentum equal to how it was before the collision
how does a safety helmet reduce the force of an impact?
increases the impact time
reducing the change of momentum per second
reducing the force of impact
how does a seat belt reduce the force of an impact
increases the impact time
reducing the change of momentum per second
and spreads out force across body
reducing the force of impact
what does it mean for an object to be elastic?
it returns to its original shape
when the forces deforming it are removed
what is Hooke’s Law?
the extension of a spring
is directly proportional to the force applied to it
until the limit of proportionality is exceeded
F = ek
what happens to a string when its limit of proportionality is exceeded?
it becomes inelastically deformed
so when the weight is removed from it
it retains its extension
