Physics

1. TORQUE
Physics 1
Second Quarter

2. OBJECTIVES
At the end of the lesson, the students will be able to:
1. define and describe operationally torque;
2. calculate the magnitude and direction of torque in a
given system; and
3. recognize the role torque in understanding the
movements of objects

3. Determine
whether the
given illustration
are balance or
not:

4. When do we say that
the object is in the
state of equilibrium
or not?

5. When do we say that the object is in the state of
equilibrium or not:
Objects in equilibrium is
at rest or moving at
constant velocity; forces
are balanced; and the
net force is equal to
zero.
Objects not in
equilibrium is in motion
and accelerating; forces
are not balanced; and
the net force is not
equal to zero.

6. How are you going to
make an object turn or
rotate?

7. How are you going to make an object turn or rotate?

8. Every time we open the door, turn on a water faucet or tighten a nut with a wrench,
we exert a turning force.
How are you going to make an object turn or rotate?

9. How are you going to make an object turn or
rotate?
Every time we open the door, turn on a
water faucet or tighten a nut with a wrench, we
exert a turning force.
Torque is produced by this turning force and
tends to produce rotational acceleration. Torque
is a measure of how much force acting on an
object causing it to rotate.

10. How are you going to make an object turn or
rotate? To illustrate:
• The object rotates about an axis,
which we call the pivot point
“O”.
• The distance from the pivot to
the point where the force acts is
called moment arm or lever arm
“r”.
• The unit of torque is newton-
meter (N.m).

11. Torque = (force) (lever arm)
τ = (F)(r) if F is perpendicular to lever arm
or
τ = (F)(r) sin ø if F is not perpendicular to lever arm
τ = 0 if F is parallel to lever arm
Torque is positive if its rotation is a counterclockwise
direction and torque is negative if it rotates clockwise
direction. If more than one force is acting on an object the
torques from each force can be added to find the net torque.
= ∑τ

12. Example:
• A 10-kilogram mass is suspended
from the end of a beam that is
1.2 meters long. The beam is
attached to a wall. Find the
magnitude and direction
(clockwise or counterclockwise)
of the resulting torque at point B.
Hint: Remember that force is
measured in newtons, not
kilograms.

13. Example:
τ = (F)(r)
τ = ( ? )( ? )
τ = _______ N-m

14. Example:
F = mg
F = (10)(9.8)
F = 98
τ = (F)(r)
τ = (98)(1.2)
τ = -117.6 Nm

15. Example:
F = mg
F = (10)(9.8)
F = 98
τ = (F)(r)
τ = (98)(1.2)
τ = 117.6 Nm, clockwise

16. ACTIVITY 1 (GRAPHING PAPER)
A. Calculate the torque on each:

17. ACTIVITY 1 (GRAPHING PAPER)
A. Calculate the torque on each:

18. ACTIVITY 1 (GRAPHING PAPER)
A. Calculate the torque on each:

19. ACTIVITY 1 (GRAPHING PAPER)
B. Solve the ff problems with complete solutions:
11. Two children push on opposite sides of a door
during play. Both push horizontally and perpendicular
to the door. One child pushes with a force of 17.5 N at a
distance of 0.600 m from the hinges, and the second
child pushes at a distance of 0.450 m. What force must
the second child exert to keep the door from moving?
Assume friction is negligible.

21. ACTIVITY 1 (GRAPHING PAPER)
For numbers 12 – 14. Forces are applied on
the beam as shown on the figure at right:
12. Find the torque about point P
produced by each of the three forces.
13. Find the net torque about point P.
14. A fourth force is applied to the beam
at a distance of 0.30 m to the right of
point P. What must the magnitude
and direction of this force be to
make the beam in rotational
equilibrium?

22. ACTIVITY 1 (GRAPHING PAPER)
15. Calculate the torque supplied by the wrench when an 8N force is
applied as shown in the figure:

23. ASSIGNMENT
Study in Advance
Moment of Inertia

24. You can now proceed to
the breakout room with
your group.

25. THE END