1. ENGR 107 – Introduction to Engineering
Forces, Moments
and
Static Equilibrium
(Lecture #7)

2. ENGR 107 - Introduction to Engineering
Force
ENGR Introduction to Engineering

3. ENGR 107 - Introduction to Engineering
Force
A force may be thought of as any influence which tends to change the motion, i.e. the velocity and/or direction, of an object.
ENGR Introduction to Engineering

4. ENGR 107 - Introduction to Engineering
Force
A force has both a magnitude and a direction. Thus, it is a vector quantity.
ENGR Introduction to Engineering

5. ENGR 107 - Introduction to Engineering
Force BX B BY R AY
R = A + B A AX
RX = AX + BX
RY = AY + BY
ENGR Introduction to Engineering

6. ENGR 107 - Introduction to Engineering
Moment
ENGR Introduction to Engineering

7. ENGR 107 - Introduction to Engineering
Moment (Torque)
The tendency of a force, F, to cause a rotation about an axis or point is called the moment, M, of the force with respect to that axis or point.
ENGR Introduction to Engineering

8. ENGR 107 - Introduction to Engineering
Moment (Torque)
ENGR Introduction to Engineering

9. ENGR 107 - Introduction to Engineering
Moment (Torque) d1 d2 P
MP = F x d
ENGR Introduction to Engineering

10. Moment (Torque) Example:
Consider different forces acting on a body, at different distances from a point of rotation on the body.
How does the force and distance effect the moment?
ENGR Introduction to Engineering

11. ENGR 107 - Introduction to Engineering
Static Equilibrium
ENGR Introduction to Engineering

12. ENGR 107 - Introduction to Engineering
Static Equilibrium
A body is in static equilibrium if the sum of all of the forces and moments acting on the body is zero.
ENGR Introduction to Engineering

13. Mathematically, this implies: S FX = 0 S FY = 0 S MP = 0
Static Equilibrium
Mathematically, this implies:
S FX = 0
S FY = 0
S MP = 0
ENGR Introduction to Engineering

14. ENGR 107 - Introduction to Engineering
Static Equilibrium
Example:
ENGR Introduction to Engineering

15. ENGR 107 - Introduction to Engineering
Static Equilibrium
Example:
ENGR Introduction to Engineering

16. ENGR 107 - Introduction to Engineering
Static Equilibrium
Example:
ENGR Introduction to Engineering

17. ENGR 107 - Introduction to Engineering
Static Equilibrium
Example:
ENGR Introduction to Engineering

18. ENGR 107 - Introduction to Engineering
Static Equilibrium
Example:
ENGR Introduction to Engineering

19. ENGR 107 - Introduction to Engineering
Static Equilibrium
Example:
ENGR Introduction to Engineering

20. ENGR 107 - Introduction to Engineering
Static Equilibrium
Example:
ENGR Introduction to Engineering