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…

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.

14. 1. Identify different types of forces, and describe how forces are measured.
support
drag
thrust
weight

15. 1. Identify different types of forces, and describe how forces are measured.
drag
thrust
weight
support
support
friction
friction
Extension

16. 1. Identify different types of forces, and describe how forces are measured.
upthrust
drag
thrust
weight

17. 1. Identify different types of forces, and describe how forces are measured.
drag
upthrust
thrust
weight
Extension

18. 1. Identify different types of forces, and describe how forces are measured.
upthrust
drag
thrust
weight

19. 1. Identify different types of forces, and describe how forces are measured.
upthrust
drag
upthrust
drag
weight
thrust
Extension

20. AP Physics 1 G11! Fs mg sin(q) mg cos(q) q
Force Components ~ Frictionless incline y x Fs
AP Physics 1
G11!
mg sin(q)
mg cos(q) mg q q

21. Draw arrows to link these correctly. Some may be used more than once.
Pushes and Pulls
Draw arrows to link these correctly. Some may be used more than once.
... measured in kilograms
... how much material you’re made of
... the same on the Earth and on the Moon
... how hard the Earth pulls on you
... about 10 N/kg
... won’t return to its original length
... measured in newtons
... less on the Moon than on Earth
The Earth’s surface gravity is...
Your mass is...
A spring stretched beyond its elastic limit ...
Your weight is...

22. Answers Pushes and Pulls The Earth’s surface gravity is...
Draw arrows to link these correctly. Some may be used more than once.
... measured in kilograms
... how much material you’re made of
... the same on the Earth and on the Moon
... how hard the Earth pulls on you
... about 10 N/kg
... won’t return to its original length
... measured in newtons
... less on the Moon than on Earth
The Earth’s surface gravity is...
Your mass is...
A spring stretched beyond its elastic limit ...
Your weight is...