1. Unit 3 Forces
Introduction

2. Definition A force is a push or pull on an object.
It’s an influence that can cause an object to be accelerated
Measured in N (Newtons)

3. Types of Forces List as many types of forces you can: “THE FORCE”
Buoyancy
Magnetism
Friction
Static Electricity
Gravity
Elasticity
Normal Force
Tension

4. Veritasium Video clip:

5. How we draw Force Vectors
Something that has both magnitude (how much) and direction (which way)
Shown as an arrow
Length is magnitude
Point is direction
Examples:
10N 5N

6. Free Body Diagrams
A free body diagram is a way of showing all the forces acting on an object at the same time using vectors.
Example:
10N 5N

7. Net Force
Net force is the overall force acting on an object
Examples:

8. Equilibrium Equilibrium is when the net force on something is ZERO.
List objects in this room that are at equilibrium:

9. Normal Force
A Normal Force is a force that is perpendicular to a flat surface.
In a simple case such as an object resting upon a table…
…the normal force on the object is equal to, but, in the opposite direction to the gravitational force applied on the object.

10. Normal Force What are the forces acting on you right now?
Are you at equilibrium?
How do you know?
Normal Force is the upward force that ensures you don’t fall through the floor.

11. What Forces Are Acting on You Right Now?

12. Equilibrium in Motion Equilibrium is when ∑ F = 0
This could be when an object is at rest, or in constant motion that isn’t changing.
Example:

13. Bill NYE!

14. Kajabe rules:

15. Four Way Tug of War:
Kajabi Can-Can finals:

16. Intro to Newton’s Second Law
Acceleration and Force

17. Refresher:

18. Force Causes Acceleration
Any object that accelerates is acted on by a push or a pull (a force!)
Acceleration depends on the net force
Examples:
As net force increases, acceleration increases
As net force decreases, acceleration decreases

19. Mass is a Measure of Inertia
The greater the mass, the greater the force needed for a given acceleration.
The greater the mass, the greater its inertia
Examples:

20. What mass isn’t…
Mass is not volume
Examples:
Mass is not weight

21. Mass Resists Acceleration

22. Newton’s 2nd Law

23. Free Fall
Objects in free fall have equal acceleration
Free fall is falling only under the influence of gravity, where other forces such as air drag can be neglected.
Example: Textbook and paper demo

24. Terminal Velocity In free fall, weight pulls down
The force of air resistance (Fair) pushes up
When they equal each other, the Σ F = 0
This means there is no acceleration
Does it stop?
No, just has constant v…( Δv = 0 )
Terminal Velocity is when there is no more acceleration due to the force of air resistance (Fair) = Force of gravity (Fg).

25. Terminal Velocity video #1

26. Terminal Velocity questions
For the video you just watched, draw a free body diagram for each of these times: (think about if the forces are equal or not)
In the plane, before jumping
After jumping before reaching terminal velocity (TV)
Once TV is reached
After opening parachute, before new TV is reached
After reaching new TV
Right when hitting the ground (for just a split second)
Once on the ground holding still

27. Terminal Velocity questions
Look at the free body diagrams you just drew. Circle those that show the skydiver accelerating.
How did you decide this?

28. Terminal Velocity video #2
Enjoy 