Force, movement, shape and momentum Flashcards
(17 cards)
What is the equation that links force, acceleration and mass
force = mass x acceleration f = ma
What is the equation that links weight, mass and gravitational field strength
weight = mass x gravitational field strength w = mg
How do you calculate stopping distance?
thinking distance + braking distance
What is stopping distance?
- stopping distance is the distance covered in the time between spotting the hazard and the coming to a complete stop
- distance it takes to stop a car is divided between thinking and braking distance
What factors affect thinking distance?
- how fast you’re going
2. reaction time (affected by drugs, fatigue, alcohol, old age)
What factors affect braking distance?
- how fast you’re going
- mass of the vehicle
- how good your brakes are
- how good the grip/friction is (depends on road surface, weather conditions, tyres)
How do moving objects reach a terminal velocity and what forces are acting on them?
frictional objects increase w speed but up to certain point
- when a object starts falling it has much more force accelerating than resistance slowing
- as velocity increases the resistance builds up
- the resistance force reduces the acceleration until the resistance = acceleration, now it can’t accelerate any more
What does the terminal velocity of a falling object react on?
shape/area
terminal velocity of any object is determined by its drag compared to its weight, drag depends of shape/area
What is Hooke’s law?
extension is proportional to force
if a metal wire is supported at the top and a weight is attached at the bottom, it stretches. the weight pulls down with force, producing an equal and opposite force.
a metal spring will also obey if a pair of opposite forces are applied to each end
What is the equation using perpendicular distance from pivot, moment and force?
moment = force x perpendicular distance from pivot
How is the linear region of a force - extension graph associated with Hooke’s law?
there’s a limit to the force you can apply for hooke’s law to stay true, the first part of the graph shows the law being obeyed (straight line relationship) but when the force becomes too great it starts to curve (elastic limit) and the object is permanently stretched
Can a shape go back to it’s original shape after passing the elastic deformation?
if an object returns to it’s original shape once the forces are removed, it obeys elastic behaviour
metals display elastic behaviour as long as hooke’s law is obeyed
What is Newton’s third law?
when you push something it pushes back just as hard but in the opposite direction, if person a pushes on person b (action force) she feels an equal and opposite force from skater b’s hand (reaction force) but a will accelerated more than b because she has smaller mass
What is the centre of gravity? How does it affect the weight of a body?
weight of a body acts through the centre of gravity
the anticlockwise movement is equal to clockwise movement and there are no downward forces acting other than the weight itself. the mass is equally spread, but if the object is not pivoted through the centre of gravity then the weigh produces a turning effect
How doe the upward forces on a beam supported at the ends vary with the positions of a heavy object placed on the beam?
the beam will not move so the upward/downward force are balanced and because the object is in the middle the upward forces are balanced but when he moves the upward forces will change
What is the equation that links momentum, mass and velocity?
p = mv
What is the principle of moments?
if an object is balanced then the anticlockwise moment s= clockwise moments and if they don’t it creates a resultant moment
