1. Take out your Free Body Diagram HW and set it at the top of your desk
Science Starter
Take out your Free Body Diagram HW and set it at the top of your desk
Which type of force acts on all objects on Earth and always points straight down?
If an object is moving with constant speed or at rest, what does this tell you about the forces?
Draw a free body diagram for the cart of eggs in the picture to the right if the cart is moving at a constant speed.

2. Today’s Agenda Science Starter FBD with Numbers Newton’s 3rd Law
Reaction Racers
Exit Quiz

3. Free Body Diagram with Numbers
Usually Free Body Diagrams will be used to solve for missing values
Need to consider 2 things:
Is the object at rest?
What are my horizontal (x) and vertical (y) forces?
Write in any missing forces and give all force value in Newtons (N)

4. The following object is at rest, what is the value of the missing force?

5. The following object is at rest, what is the value of the missing force?

6. The following object is at rest, what is the value of the missing force?

7. The following object is at rest, what is the value of the missing force?

8. Free Body Diagram with Numbers
Important Equations to know:
Force of Gravity (FG) = mass (kg) * gravity on planet (Earth is 10)
Force of Friction (Ff) = coefficient * Normal Force

9. Example Question #1 FN= FG=500 N
A girl has a mass of 50 kg and is sitting on the ground. Draw the FBD with numbers for this scenario
FG= (50)*(10)= 500 N

10. Example Question #2 FN= FG=50 N
A 5kg box is pushed to the right with a force of 20 N, but does not move. Draw the FBD for this scenario.
Ff =20 N
FA =20 N
FG= (5)*(10)= 50 N

11. Newton’s 3rd Law Demonstration
If I stand and throw the ball, what will happen?
If I stand and throw a heavier ball, what will happen?
Why did the heavy ball produce this effect?

12. Newton’s 3rd Law
States: To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.
In other words: If an object exerts a force on a second object, the 2nd object exerts a force back to the first!
Also: This is why unbalanced forces cause motion change!

13. Reaction Racers!
You will build a “Rxn Racer” to demonstrate Newton’s 3rd Law
You need to consider things like force, mass, and friction
Design the best car you can and we will have a race tomorrow…
Be ready to start your engines!

14. Exit Quiz & Homework FBD w/ Numbers
Same exact scenarios yesterday’s homework, just add numbers to every force that you draw.
Remember to use your equations and balance all forces!
Dog, Car, & Baseball tomorrow…
How do the reaction racers demonstrate Newton’s 3rd Law?
(use as much space as you need, to explain your answer)