1. October 18, 2017
Forces

2. Drill - Take out Unit 1 Vocabulary Chart
What is the unit for force?
Who discovered the force of gravity?
Name the 8 forces we discussed yesterday.

3. Legend has it that a young Isaac Newton was sitting under an apple tree when he was bonked on the head by a falling piece of fruit, a 17th- century “aha moment” that prompted him to suddenly come up with his law of gravity. In reality, things didn’t go down quite like that. Newton, the son of a farmer, was born in 1642 near Grantham, England, and entered Cambridge University in 1661.
In 1667, he was in his father’s orchard when he witnessed an apple drop from a tree. There’s no evidence to suggest the fruit actually landed on his head, but Newton’s observation caused him to ponder why apples always fall straight to the ground (rather than sideways or upward) and helped inspire him to eventually develop his law of universal gravitation.
In 1687, Newton first published this principle, which states that every body in the universe is attracted to every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

4. Newton’s First Law
An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.
“An object in motion will remain in motion.”
“An object at rest will remain at rest.”

5. Newton’s Second Law
Force = mass x acceleration
F = ma

6. Newton’s Third Law “Every action has an equal, but opposite reaction.”
When two objects interact, they exert an equal amount of force on each other.
The forces on the objects are in opposite directions.
This law is ALWAYS true.

7. Acceleration
Acceleration is a vector quantity that describes how quickly the velocity of an object is changing.
Symbol: a
Units: m/s2
Relationship: average acceleration = amount velocity changed
a = Dv/Dt

8. Example 1
What is the acceleration of a car that travels east at a constant speed of 60 mph for 3 hours? Answer: ZERO!! Acceleration describes how quickly velocity is changing and neither the magnitude or direction of this car’s velocity are changing.

9. Example 2
What does it mean if a car traveling forward experiences a negative acceleration?

10. Interaction Maps Include any objects that are relevant to the problem.
Draw a line connecting any two objects that are interacting with each other. Label the line with the name of the interaction type.
Draw a “system boundary”.
Each interaction line crossing the system is a force acting on it.

11. Interaction Maps TREE PERSON CHAIR EARTH FLOOR
Example: A person pushes a chair across the floor.
TREE
PERSON
APPLIED
FLEX
GRAVITY
GRAVITY
CHAIR
FRICT.
FLEX
GRAVITY
EARTH
FLEX
GRAVITY
FLOOR
FRICTION
FLEX

12. Simpler Version CHAIR PERSON EARTH FLOOR
Example: A person pushes a chair across the floor.
APPLIED
CHAIR
PERSON
GRAVITY
FLEX
EARTH
FRICTION
FLOOR

13. Free Body Diagrams Draw a box to indicate your system.
Add an arrow to your diagram to indicate each force acting on the system.
The arrows should point in the direction of the force.
The length of the arrows should indicate the size of the force.
The arrows should be labeled with the name of the force.

14. Example: A person pushes a chair across the floor
Fflex (floor on chair)
Ffriction (floor on chair)
Fapplied (person on chair)
Fgravity (earth on chair)

15. Practice – Draw a free body diagram for each
An empty bucket is lowered into a well at a constant speed with a rope.
After being hit with a hockey stick a hockey puck slides across ice to the right toward the goal.
A falling sky diver and his parachute slow down once his chute opens.

16. Motion Project Proposal
Draft: Monday, October 23 (for my feedback)
Final: Friday, October 27
Must include in proposal:
Video URL
Description of motion in video
Plan for analyzing motion
Plan for presenting motion

17. Homework
Unit 1 Take-Home Test
Motion Project Proposal Draft