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MOVING IN CIRCLES
Objects will move in a straight line, at constant
velocity, unless a force acts to change their speed
or direction.
A force at right angles to the direction of motion
will make an object start to move in a circle.
VELOCITY
FORCE
Actual curved path
The force needed to move in a circle is always
directed into the centre of the circle.
VELOCITY
FORCE
We call this a
CENTRIPETAL FORCE.
For planets orbiting the
Sun, GRAVITY provides
this force.
Although an object orbits at constant speed, its
direction keeps changing, hence its velocity will
have to change.
Change of velocity is called acceleration, so this is
why we require an inwards centripetal force
(remember that: F = ma)
NB – It accelerates but it does not get any faster!!!
All objects moving in a circle have a centripetal
force that keeps them changing direction
constantly:
Planets in orbit = GRAVITY
Car going around a roundabout = FRICTION
Swinging a hammer = TENSION
The Centripetal force will need to be bigger if an
object:
Moves at a higher VELOCITY
Travels in a smaller RADIUS circle/orbit
Has more MASS
Centripetal force explains why satellites stay in
orbit at a constant height above the Earth
Centripetal force also explains why planets stay in
orbit at a constant distance from the Sun