1. DO NOW QUESTION What forces are present on the monkey?

2. Unit 3: Forces Forces in Equilibrium
Students will be able to (SWBAT)… identify forces in daily life.

3. Skydiving
3:40

4. The floor exerts an equal and opposite force upward on the box called the normal force.
The box is in equilibrium at 0N.

5. Vector quantities
A vector is a quantity that includes both magnitude and direction.
Magnitude: shows the quantity or strength (Number & Unit).
Force vectors have the same units as force – Newtons
Vectors can combined.

6. The force vector We define positive direction as up or right.
We define negative direction as down or left.
A vector must be drawn to scale to show magnitude.
EX: 1 cm = 1 N or 1 graph square = 1N.

7. Free-body diagrams (FBD)
A free-body diagram is a diagram that uses vectors to show all of the external forces acting on an object.
A free-body diagram of a book shows only the forces acting on the book.

8. Free body diagrams (FBD)
A free-body diagram for a monkey hanging from two ropes includes all forces acting on the monkey.
The tension forces of the ropes (F1 and F2) acts on the monkey, as well as gravity (Fw).

9. The net force & Free body
Consider the forces…
Book weighs 30 N
Table weighs 200N

10. Types of Forces

11. This is the object’s weight– it always points straight down.
Gravitational force
Symbol: Fg
This is the object’s weight– it always points straight down. Fg

12. Normal force Symbol: FN
This is the upward force that is perpendicular to the surface an object sits on. Fg

13. FN
Applied force
Symbol: Fapp
This is the push or pull put on an object.
In the example, you’re pushing the object to the left.
Fapp Fg

14. A chandelier hanging from the ceiling by two cables
Tension FT
This is for hanging objects – in the direction the string is pulling the object. FT FT Fg
A chandelier hanging from the ceiling by two cables

15. This goes in the opposite direction of motion.
Friction Ff
This goes in the opposite direction of motion.
Air resistance = friction FN
Fapp Ff Fg

16. Air resistance
When something falls through air, the air exerts an additional force.
This force, called air resistance, acts opposite to the direction of the object’s motion.

17. Terminal velocity
Objects only accelerate until the force of air resistance equals the force of gravity.
The net force then becomes zero and the object reaches a constant velocity called the terminal velocity.

18. Forces and equilibrium
When the net force on an object is zero, we say the object is in equilibrium.
Newton’s first law says an object’s motion does not change unless a net force acts on it.
If net force is 0N, then the object does not accelerate (move).

19. Forces and equilibrium
Gravity is a force that always present.
If is not moving, normal force is present.
Gravity always points down to Earth.
In mathematics, the normal force is means perpendicular (90 degrees).

20. Example of Drawing Free body Diagrams
A skydiver is descending with a constant velocity. Consider air resistance. A free-body diagram for this situation looks like

21. Example of Drawing Free body Diagrams
A rightward force is applied to a book in order to move it across a desk with a rightward acceleration.
Consider frictional forces. Neglect air resistance. A free-body diagram for this situation looks like this:

22. Review: Draw vectors to scale
1. Draw a vector that is 5N to the right.
2. Draw a FBD with a gravitational force of 1N and a normal force of 2N. Use a scale!

23. Review: Describe and distinguish between different types of forces.
What force pulls objects toward the ground?
What force is a support force?
Air Resistance is an example of this type of force.
Weight is measured using this force.

24. Review: Create & analyze free body diagrams
Draw a free body diagram of this cheerleader in the air.