2.4 - Further motion concepts Flashcards
What are the unit used for momentum?
kg m/s
What is momentum?
Momentum is about how much motion an object has
What is the law of conservative momentum?
Total momentum before interaction = Total momentum after interaction (if there are no external forces acting)
How can the momentum of an object can change?
the object speeds up or slows down
the object changes direction
The time taken for the change in momentum to occur is proportional to the…
Resultant force felt by the object. ( Newton’s second law: F=ma, where mass x acceleration is the rate of change of momentum
What is an alternative name for the turning effect of a force?
A moment
What distance measurement is used when calculating a moment?
The perpendicular distance from the pivot to the line of action of the force
If an object is in rotational equilibrium, what can be said about the moments acting on the object?
The clockwise moments are equal to the anticlockwise moments
What force is needed to get a 25 kg stationary bicycle moving at 12 m/s in 5 s?
Momentum at start = 0 × 12 = 0 kg m/s
Momentum at end = 25 × 12 = 300 kg m/s
Change in momentum = 300 – 0 = 300 kg m/s
Force = change in momentum ÷ time = 300 ÷ 5 = 60 N
Energy can not be created or destroyed but it can be transferred into heat/sound. This means that often kinetic energy is lost from colliding objects in a collision.
What is an elastic collision?
What is an inelastic collision?
Elastic collision: no loss in KE
Inelastic collision: loss in KE
An object being fired from a cannon is also a collision where momentum must be conserved. As the momentum before the collision is zero, the momentum after the collision is zero. In physics, this type of event is termed an _____
explosion
What is recoil?
Backwards movements produced by a force exerted on an object
What does the size of the moment depend on?
the size of the force applied
the perpendicular distance from the pivot to the line of action of the force
This explains why less force is needed to open a door by pushing at the side furthest from the hinge than at the side closest to the hinge. To push at the hinge side of the door requires more force to be exerted because the distance is smaller
A spanner is used to undo a nut. A force of 25 N is applied to the end of the spanner, which is 10 cm away from the centre of the nut. Calculate the moment when the spanner is horizontal
10 cm = 10 ÷ 100
= 0.10 m
moment = 25 × 0.10
= 2.5 Nm
A see-saw has a pivot in the middle, which means that:
the person on the right exerts a force downward – which causes a clockwise moment
the person of the left exerts a force downward – which causes an anti-clockwise moment
If the people are identical weights and sit identical distances from the pivot, the see-saw will balance. This is because the total clockwise moment is balanced by the total anti-clockwise moment.
The see-saw can still be made to balance even if the people are different weights. How do you do this?
To do this, the person who weighs the most must sit closer to the pivot. This reduces the size of the moment so the opposing moments are once again balanced.
