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Flashcards in Forces and Motion Deck (17)
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What is Hooke's Law?

The extension of strechted spring is proportional to the load or force applied to it.


At what point goes Hooke's law change?

When you have added so much force to the spring that it has reached its elastic limit. This means it will be permanently stretched and not return to its natural length.


What is elastic behaviour?

When a material can return to its original shape once forces have been removed.


What is an orbit?

An orbit is the balance between the forward motion of an object on the force pulling it inwards. The force that pulls it inwards is provided by the gravitational pull of the planet it is orbiting.


Describe the orbit of a comet.

Comets orbit the sun but have very ellpitical (elongated) orbits. A comet travels much faster when its nearer to the sun that it does in more distant parts of its orbit.


Why do comets speed up the closer they get to the sun?

Because as it gets closer to the sun there is an increased pull of gravity.


What is the equation for orbital speed?

orbital speed = (2 x pi x orbital radius)/ time period


What is the principel of moments?

Total anticlockwise moments = total clockwise moments
(clockwise and anti clock wise being each end of the pivot)


What will happen is the total clockwise and anticlockwise moments are not equal around a pivot?

There will be a resultant force, so the object will turn.


What is centre of gravity?

The point through which the weight of the body acts. A freely suspended object will swing until its centre of gravity is vertically below the point of suspension.


Describe how a freely suspended object would come to its rest position.

Freely suspend an object from a point.
1) The objects weight acts at a distance from the pivot, which creates a moment around the pivot.
2) This makes it swing...
3) Until the centre of gravity is at its lowest (i.e. directly under the pivot)
Note: It reaches a rest position because there's no moment acting on it anymore - the pivot is in line with the line of action of force.


What is the law of momentum?

Momentum before = momentum after


Describe how an object reaches terminal velocity as it falls.

When free falling objects first set off they have much more force accelerating them than resistance slowing them down.
As their velocity increases the resistance acting on it (i.e. air resistance) builds up.
This gradually reduces the acceleration unti eventually the resistant force is equal to the accelerating force and then it won't be able to accelerate anymore.
It will have reached its maximum/ terminal velocity.


What affects the terminal velocity of an object?

Its shape and surface area.


Describe how to read a velocity-time graph.

- Gradient = acceleration
- Flat sections = steady speed
- The steeper the graph the greater the acceleration
- Downhill sections are deceleration
- The area under any section of the graph is the distance travelled
- A curve means changing acceleration


How to calculate the acceleration from a velocity-time graph

acceleration = gradient
gradient = rise/run


Decribe how to read a distance-time graph

- Gradient = speed (so to speed use rise/run)
- Flat sections = object has stopped
- The steeper the graph, the faster it's going
- Downhill sections mean its going back towards it's starting point
- Curves represent acceleration or deceleration
- A steepening curve means it's speeding up and a leveling off curve means it's slowing down