1. Equilibrium

2. Force Force is A push or pull on an object.
A vector with magnitude and direction.
Force is not
Energy.
Power.
Momentum.
Velocity.

3. Fundamental Forces Gravity is a fundamental force.
It acts upon objects from a distance away from the source (such as the Earth).
There are two other fundamental forces.
Electroweak force is common in everyday life.
Electricity
Magnetism
Light
Radioactive decay
Nuclear force is uncommon in everyday life.
Nuclear fission (nuclear power plants)
Nuclear fusion (stars)

4. Contact Forces Many forces are due to contact between objects.
Kick a ball
Push with a bulldozer
Tug from a rope
Friction due to the ground
The actual force is electricity, but the atoms are so small we can treat the forces as coming from contact by larger objects.

5. Newton’s Laws
Ancient scientists looked to the natural properties of objects.
Motion was a result of the object’s properties.
Newton defined motion based on forces acting from outside an object.
Motion was the result of external forces.
Three laws were used to define the behavior of forces on objects.

6. First Law: Law of Inertia
An object continues at rest, or in uniform motion in a straight line, unless a force is imposed on it.
This describes constant velocity, including zero.
No change means no force, and vice versa.
no force
rocket
constant velocity

7. Zero Net Force
An object at rest with no net force is in static equilibrium.
The net force is due to the sum of forces acting on the object.
The forces are vectors

8. Static Forces
An advertising sign weighs 210 N. It is supported from a post with a horizontal beam, and by a chain making an angle of 35 from the horizontal. What is the force in the chain?
q = 35º
Newton Legal
W = 210 N

9. Vector Forces With no motion, forces must sum to zero.
Identify forces on the sign.
C is the force on the chain
B is the force on the beam
W is the weight
Vector sum is zero.

10. Force Components To find the values, use components
Find the vertical components for the force on the chain.
Cy = C sinq
Wy = -210 N
0 = Cy + Wy = C sinq + Wy
C = -Wy / sinq = 370 N
Use horizontal components for the force on the beam.
0 = Bx + Cx = Bx + (-C cosq)
Bx = C cosq = 300 N Cy
q = 35º Bx Cx
Wy = -210 N

11. Constant Velocity next Constant velocity means no change in motion.
Dynamic equilibrium applies in states of constant, non-zero velocity.
Zero net force used here:
FN + Fg + Fy = 0
Fx + Ffr = 0 v0 FN
Ffr Fx Fg Fy
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