1. Some Particular Forces
Weight = mg
(direction: downward)
mass
9.8 m/s2
Free body diagram: mg
Mass and weight are not the same thing!
Mass is an intrinsic property of an object
Weight depends on the value of gravity

2. The Support()Force Fs= support force S F = 0, since at rest mg
Any object in contact with a surface experiences a support force (Fs) perpendicular to that surface
In the picture above: Fs = mg
But this is not always the case!…….

3. Solve Unknowns Determine the magnitude of the forces acting on the
2 kg masses at rest below.
∑Fx = 0 and ∑Fy = 0
mg = 20 N
FN = 20 N
Solve Unknowns
∑Fy = 0
FN - mg = 0
FN = mg
= 20 N

4. Examine the following diagrams and write 2-3 facts and figures about them…
Understand this page and you have…

5. Tension (T) – force applied by a string or rope
Ex:
5 N
T = 5 N
We say “the tension in the string is 5 N”
The tension is the same throughout a string, even when it passes over pulleys: T

6. Ex: A person pulls a crate across the ice with a rope
Find the horizontal acceleration of the crate.
15 N
m=35 kg
30

7. Static friction (fs) – keeps objects from moving
Friction (f) – a force that opposes motion between two surfaces in contact
motion
(or attempted motion)
friction
Two types of friction:
Static friction (fs) – keeps objects from moving
Kinetic friction (fk) – opposes motion while moving
Both depend on:
Surfaces in contact
Amount of normal force (FN)

9. Heat energy is always produced.
Friction is a force. It occurs when two surfaces rub together.
Heat energy is always produced.

10. Friction always opposes motion.
Drag
Thrust

11. Streamlining objects can reduce this effect.