Transcript NOTES AP1 Angular Motion

Angular Motion
AP Physics 1
Revolving Motion vs Rotating Motion
The Earth ____________ around the Sun
while _____________ around an axis.
Revolving
Rotating
What is a rigid body?
A rigid body is an object __________________
_____________________________________
_____________________________________.
Examples:
3 Motions of a Rigid Body
1.Translational Motion:
Examples:
2. Rotational (Angular) Motion:
Examples:
3. Combination Motion:
Examples:
Translational Motion to Angular Motion
Translational Motion Variable
Angular Motion Variable
∆x (m)
Ѳ (rads)
v (m/s)
ω (rad/s)
a (m/s2)
α (rad/s2)
v = ωr Speed of a point on the rigid body
a = αr
Acceleration of a point on the rigid body
Let’s take a look at our reference pack……
Example: Convert the following
a. 60⁰ to radians
c.
1500 rpm to rad/s
b.
30 revolutions to radians
Example: A tire with a diameter of 90 cm starts from rest and makes 15
revolutions in 5 s.
a.
b.
c.
d.
What is the angular acceleration of the tire?
What is the angular velocity of the tire at the end of the 5 seconds?
What is the translational acceleration of a point on the outside edge of the tire?
What is the translational velocity of a point on halfway to the outside edge of the
tire? How would that velocity compare to the velocity of a point on the outside edge
of the tire?
Torque, (τ)

analogous to force in that force produces linear acceleration and
torque produces rotational, or angular acceleration
  rF sin 
Line of action – extended line collinear with the force
Lever arm – distance l between the line of action and the axis of rotation,
measured on the line perpendicular to both.
The “sin θ” term comes from the fact that only forces tangential to the circle
(of radius r centered on the axis of rotation) cause torque:
Thus, radial forces do not cause torque.
Direction: the torque is positive if the force tends to produce a
counterclockwise rotation about the axis, and negative if the force tends
to produce a clockwise rotation.
Units: mN (meter -Newton)
Example:
Two forces act on a wheel, as shown below. The wheel is free to rotate without
friction, has a radius of 0.42 m, and is initially at rest. Given that F1 = 12 N
and F2 = 9.5 N, find (a) the torque caused by F1 and (b) the torque caused by
F2. (c) In which direction does the wheel turn as a result of these two forces?
Gravitational Torque and the Center of Gravity
We won’t prove it but……..
The weight of an object acts at a single special point on the
object called its ____________________________.
Facts about the center of gravity of an object:
Images of center of gravity…..
Finding the Center of Gravity