1. FORCES Write 5 examples of an object accelerating
In each example, what causes the object to accelerate?

2. FORCES
Newton’s Three Laws

3. Newton’s First Law of Motion
Law of Inertia
Inertia is a property of matter.
Inertia is an object’s tendency to resist a change in motion.
The law states:
An object at rest will stay at rest unless a net force acts upon it.
An object in motion will stay in motion unless a net force acts upon it.

4. Egg Drop Experiment
What will happen to the egg when the pie tin is hit?
Why would it do that?

5. Newton’s Second Law of Motion
Force = mass x acceleration
F=ma
Force and acceleration are directly proportional. More Force means more acceleration.
Mass and acceleration are inversely related. With the same amount of force, an object with greater mass will have less acceleration

6. Ball Bearing Race
Which ball moved farther?
Why did it move farther?

7. Newton’s Third Law of Motion
States that:
For every force there is an equal and opposite reaction force.
When you push against something, it pushes back!

8. Third Law Examples Space Shuttle Launches Jumping, Swimming, Running
Gravity
Swings

9. TYPES OF FORCES Fg = Gravity! Fa = Applied Force Ff = Friction
FN = Normal Force
Ft = Tension Force
Fs = Force of a spring
Fair= Air Resistance
Fnet = The sum of all forces acting on an object.

10. About Forces All forces: Obey the three laws
Are measured in Newtons (N)
1 Newton = 1 kg * m/s2
Note: mass is in kilograms
Have a magnitude and direction
They’re vectors!
Are represented with arrows.

11. Force of Gravity Always present in a downward direction.
Also known as Weight
Can be calculated using Newton’s Second Law: F=ma
Fg=m*ag (ag=9.8m/s2)

12. Gravity Example Your cat has a mass of 1.6 kg. What is it’s weight?
Fg = ma
Fg = 1.6kg * 9.8m/s2
Fg = kg*m/s2 = N

13. Normal Force Always perpendicular to the applied surface.
Equal to the total force applied to that surface

14. Normal Force Calculation
You headbutt someone with an applied force of 10 N. What is the normal force applied to your head?
FN = 10N

15. Tension Force Always in the direction of an object being pulled.
Used with ropes, strings, cables, etc.
Can either be used when pulling or hanging an object.
When hanging, Ft is equal to Fg
Ft has an upper limit, if that is exceeded, the cable/string will snap!

16. Tension Force Calculation
A 4000N block is hanging from a crane. What is the Tension Force applied by the cable?
Ft = 4000N

17. Friction Always acts in the opposite direction of the intended motion.
Friction must be overcome for an object to accelerate across a surface.
Two types of Friction:
Static Friction – opposes the start of motion (before an object is moving)
Kinetic Friction – opposes the current motion of an object
Static Friction is larger than Kinetic Friction

18. Calculating Friction Ff=μFN
μ – (pronounced “Mew”) - Coefficient of Friction
Doesn’t have units
Value is different for different surfaces
Rough surfaces have a higher μ

19. Friction Calculation
The coefficient of friction for a object sliding on a horizontal concrete floor is .62, if the object weighs 20N, what is Ff?
Ff=μFN
Ff= .62 * 20N
Ff= 12.4N

20. Air Resistance
When an object moves through air, the air pushes back on the object.
Acts in the direction opposite the objects motion
Fair is normally very small, so we can ignore it, except when an object is falling.

21. Free Body Diagrams Used to show the forces acting on a body.
Use a box (or dot) to represent an object.
Draw the forces that effect the object
Remember that if the object isn’t accelerating, Fnet=0.

22. Free Body Diagram Practice
A book is sitting on a desk

23. Free Body Diagram Practice
A book is being pushed along a desk.

24. Free Body Diagram Practice
A ball is hanging from a string

25. Free Body Diagram Practice
The same ball, but the string has been cut.