Chapter 10 * circular motion
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Transcript Chapter 10 * circular motion
10.1 – ROTATION & REVOLUTION
Rotation – object that turns
on its own axis
The whole object is
connected
The earth spinning
Revolution – does not turn
on its own axis
Objects are not connected
The earth in its orbit
10.2 – ROTATIONAL SPEED
Linear Speed (tangential speed) – the distance covered in a
specific amount of time
Varies as distance from axis changes
Rotational Speed – the number of rotations (revolutions) per
time
The same for all distances from axis
Expressed as RPM
10.2 – Rotational Speed – Cont.
Tangential speed α distance
from axis & rotational speed
v = 2πr / T
Tapering causes linear speed
to vary depending on radius
Therefore the cup changes
direction
10.2 – Rotational Speed – Cont.
Railroad trains have tapered wheels to cause the train to
change direction
The smaller diameter wheel travels slower and causes the
train to move in that direction
10.3 – CENTRIPETAL FORCE
Accelerations are caused by:
speeding up, slowing down or
changing direction –
centripetal acceleration, ac
A net force causes an object to
follow a circular path
It is always directed towards the
center
Centripetal Force
“center seeking”
Fc = m v2 / r
Not a “real” force
10.3 – Centripetal Force – Cont.
Centripetal Force is always caused by other “real” forces –
Friction, normal, weight, tension
Our task is to find out what the “real” force is and make
it equal to centripetal force
10.3 – EXAMPLES OF CENTRIPETAL
FORCE
Tension is a string connected to a
can spun in a circle
Friction between two surfaces
provide the necessary centripetal
force
In a centrifuge, normal force of the
test tube causes it
If “real” force is not sufficient, the
object does not follow a circular
path (meeting the requirements)
10.4 – CENTRIPETAL &
CENTRIFUGAL FORCES
Centrifugal force – the
apparent “center
fleeing” force an object
experiences
All objects have inertia
and want to go in a
straight line
Something forces them
to change direction
Always acts radially
10.5 – centrifugal force in a
rotation reference frame
What if you are a bug
inside a spinning can
To it, there is an force
pushing it outwards
(centrifugal)
It is not real, as the
spinning slows and
stops, so does this
imaginary force