1. -Clean paper (2) / pencil -Friction/Gravity Notes WS
You need:
-Clean paper (2) / pencil
-Friction/Gravity Notes WS
-Force Practice Problems (free body diagrams)
Nov. 27, 2018
Warm Up:
What is free fall? Will it happen naturally on Earth? (explain)
I CAN: identify the basic laws of motion (Newton’s)

3. November 2018 Force/Motion Force/Motion Force/Motion Force/Motion
Friction / Gravity
Newton’s Laws
Simple Machines
Force/Motion
Force/Motion
Force/Motion

4. December 2018 TEST!! Force/Motion Weather Weather Weather Weather

5. Energy Energy is what makes things move or change. What do you know?
What do you think?
Energy is what makes things move or change. PE KE
1. Ask students to share examples of energy and to explain what they think about it. Accept all answers without correction. 2. Hold a book a few feet above a table, as still as possible. Ask the class if the book has energy? Again, accept all answers. Drop the book and repeat the question. 3. Introduce a working definition of energy: “Energy is what makes things move or change.” Explain that we will explore energy during the next several activities.
MECHANICAL ENERGY

6. How can we describe motion?
Motion can be described by:
DISTANCE (how far did it travel?)
TIME (how long did it travel?)
SPEED (how fast did it travel?)
DIRECTION (which way did it go?)
VELOCITY (speed + direction)
ACCELERATION (does the motion change?)

7. No Motion

8. FAST vs. SLOW
FAST
SLOW

9. Speeding Up
Slowing down

10. A FORCE is a PUSH or PULL in a particular DIRECTION.
FORCES
A FORCE is a PUSH or PULL in a particular DIRECTION.

11. FORCES
If the forces cancel each other out, and do not cause the object to move, the forces are said to be BALANCED.
If the forces don’t cancel each other out – 1 force is stronger than the others – the forces are UNBALANCED and will cause a CHANGE IN MOTION.

12. FRICTION

13. What is Friction?
Friction is a force that two surfaces exert on each other when they rub against each other.
The direction of the friction force is always OPPOSITE to the direction of the motion.
Direction of Motion
Friction Force

14. Direction of Intended Movement
Types of Friction
Static Friction opposes the motion of an object that is at rest
To make the object move, you have to exert a force larger than the force of static friction.
Direction of Intended Movement
Static Friction Force

15. Sliding Friction Force
Types of Friction
Sliding friction occurs when two solids slide over each other.
Sliding friction makes car brakes work and stops athletes from slipping.
Direction of Slide
Sliding Friction Force

16. Types of Friction
Rolling friction occurs when an object rolls across a surface.
Rolling friction is easier to overcome than sliding friction for the same materials.
Direction of Motion
Friction Force

17. Types of Friction
Fluid friction occurs when a solid object moves through a liquid or gas.
Air resistance is a type of fluid friction.
Direction of Motion
Friction Force

18. & AIR RESISTANCE The physics of falling
GRAVITY
& AIR RESISTANCE
The physics of falling

19. Universal Gravitation
Actually in science, gravity is a force of attraction that acts between ALL objects (the earth, you, the desk, a book)
The force of gravity is much STRONGER for LARGER objects (more mass).

20. Universal Gravitation
Because the Earth is by far, the largest and closest object around, it has the greatest force of attraction...
So, no matter where you are on earth, all things fall to the ground due to gravity…

21. What is “free fall”?
When gravity is the ONLY force acting on an object, it is in free fall.
In that case, gravity is an UNBALANCED FORCE which causes the object to accelerate.

22. (Spf – Spi) Acceleration = time D S T Math cheat sheet Formula
Substitution
Final answer with unit!

23. Acceleration due to Gravity
Calculate the acceleration of an object in free fall.
A = Final speed – initial speed
time
A = 50 m/s – 0 m/s
5 s
Acceleration = 10 m/s2

24. Objects in Free Fall Do all objects fall at the same rate?
ALL objects in free fall travel at the same rate, regardless of mass!
In free fall, heavy objects and light objects fall at the same rate!

25. So, which will land first?
WHY does the penny land first?
Remember the force that opposes motion (slows things down)? FRICTION!
Falling objects experience friction with the air called AIR RESISTANCE that slows them down.

26. Air Resistance
The larger the object (more surface area), the more air resistance.
That’s why parachutes work! The upward force of the air acting on the LARGE parachute slows you down as you fall.

27. Air Resistance Draw a diagram showing the forces…
Gravity
Draw a diagram showing the forces…
Downward force of gravity is same on both.
Upward force of air resistance is greater on the feather.
The net force (down) is greater on the penny.
Net Force on Penny
Net Force on Feather

28. That’s why astronauts weigh less on the moon!
Gravity on the moon?
The force of gravity is much weaker on the moon because…
It is much farther away from earth.
The moon is much smaller than earth.
That’s why astronauts weigh less on the moon!

29. Gravity Review
Gravity is the force that pulls all objects down to the earth.
When gravity is the ONLY force acting, ALL objects accelerate at a rate of 10 m/s2.
Mass doesn’t matter – in free fall, heavy objects and light objects fall at the same rate!

30. Air Resistance Review
Some objects take longer to fall – they are slowed down by FRICTION with the air called AIR RESISTANCE.
The larger the surface area, the greater the force of air resistance pushing up.
Without air resistance, all objects would fall at the same rate…

31. Draw a free body diagram of the sky diver and label ALL the forces.
Gravity = 1000 N
Air Resistance = 800 N
What is the net force?
Air Resistance = 800 N
Net Force = 200 N
Gravity = 1000 N