### Homework:

```Predict the readings on the scales:
0
30
?
0
10
30
20
?
20
1.0 m
0.5m
Mbar = 1.0 kg
1.0
kg
10
Predict the readings on the scales:
0
30
0
10
20
10 N
30
20
1.0 m
0.5m
Mbar = 1.0 kg
10
1.0
kg
10 N
Now predict the readings:
0
30
?
0
10
30
20
20
1.0 m
0.8m
Mbar = 1.0 kg
a=0
?
1.0
kg
10
Which force is most effective in
causing rotation?
F2
standard meter stick
F1
standard pivot point
standard frictionless pond
Now which force is most
effective in causing rotation?
F2
standard meter stick
F1
standard pivot point
standard frictionless pond
Definition of torque
t = rFperp
In practice….
F = 200 N
t = r F = (3 m)(200 N)
= 600 m - N
r=3m
Pivot
Useful force method: only the
component Fperp causes torque.
F
q
q
F sin q
r
t = r (F sin q)
= r Fperp
Fixed Pivot
Point
Torque
• A torque is produced when a force is
applied with “leverage”.
• net torque causes angular acceleration
• Only the perpendicular force contributes
to the Torque.
Torque
• net torque causes angular acceleration if
the force is applied “off center”
• If net torque = 0, angular velocity() =
constant.
• Doubling the net torque doubles angular
acceleration ().
Let’s practice:
0
30
?
10
20
pivot
1.0 m
200 N
200 N
Let’s practice:
0
30
?
10
400 N
20
pivot
1.0 m
0.5m
200 N
Linear equilibrium:
a=0
Fleft = Fright
100 N
??? N
150 N
Rotational equilibrium
=0
0
30
?
10
800 N
20
t1 = t2
pivot
1.0 m
0.25m
200 N
Let’s solve the problem:
0
30
?
0
10
30
20
?
20
1.0 m
0.8m
Mbar = 1.0 kg
a=0
=0
 Fnet = 0
 tnet = 0
1.0
kg
10
t1 = t2
(10 N)(.5 m) + (10 N)(.8 m) = TR(1 m)
TL = 7 N
TR = 13 N
TL
0.8m
Pivot
0.5m
10 N
10 N
TR
Let’s solve the problem:
0
30
?
0
10
30
20
?
20
1.0 m
0.6m
Mbar = 1.0 kg
a=0
=0
 Fnet = 0
 tnet = 0
1.0
kg
10
```