forces and motion Flashcards
what does Hooke’s Law state
extension of spring or wire is PROPORTIONAL to the load causing the extension
when is Hooke’s Law obeyed
when data creates a straight line through the origin
what equation works ONLY IN EQUILIBRIUM
F1d1 + F2d2 = F3d3
what is the principle of moment
in equilibrium, moments anticlockwise are equal to moments clockwise about the same point
equation linking moment, force and distance perpendicular from the pivot
moment = force x perpendicular distance from pivot
how to find the centre of gravity in an irregular shape
1) find a weird shape
2) get clamp stand and clamp a pin in
3) pin the shape and let it swing freely until stationary
4) wrap a plumb line around pin and let swing freely without touching the shape
5) draw a straight pencil line in the direction of the plumb line
6) repeat with pin in different area of shape
7) mark where lines meet giving you the centre of gravity
what are the 3 types of equilibrium
stable equilibrium
unstable equilibrium
neutral equilibrium
what is an objects “elastic limit”
the point at which an object stops acting “elastically” and starts behaving “plastically”
do elastic bands obey Hooke’s Law
no
why do objects fall at constant velocity
- weight acts downwards toward the ground
- air resistance acts upwards
- causing forces to be balanced
- F = ma
- no acceleration due to no resultant force
what is the conservation of momentum
initial momentum = final momentum
what is newton’s third law
for every force there is an equal and opposite reaction
What are balanced forces?
- Equal and opposite forces
- Acting on the same object
- Eg Weight and Air resistance
What are Newton’s third law pairs? (or action-reaction pairs)
- Equal and opposite
- Acting on different objects
- Eg Car pushes on road, road pushes (same force) on car
how does a DC motor work
- current in coil creates magnetic field
- magnetic field around coil interacts with magnets to produce a force
- LH has upward force, RH has downward force - causing turning motion
- every half-rev, the brushes swap each half of the commutator
- which reverses the direction of current and keeps the coil turning
