1. Forces
Chapter 3

2. Force, Mass, & Acceleration
More force on an object = more acceleration
The acceleration of an object depends on its mass as well as the force exerted on it.
Ex: thrown softball vs baseball

3. Newton’s 2nd Law of Motion
The acceleration of an object is in the same direction as the net force on the object
Force is Measured in Newtons
Equation: Acceleration = (net)force/mass or a = f(net)/m = m/s
To find force: f = ma
To find mass: m = f/a

4. Friction
A force that opposes the motion of objects that touch or between 2 objects in contact
Air resistance: friction acting on objects moving through the air
Objects with larger surface areas = greater air resistance
Also affected by size, shape, and speed

5. 3 Main Types of Friction
1.) Static Friction: force that prevents two surfaces from sliding past each other.(Box across the floor)
2.) Sliding: forces that are caused by an object as it slides over a surface
3.) Rolling: friction force that acts on rolling objects

6. Air Resistance Type of fluid friction Falling, running, …
More surface exposed = more resistance
Ex: flying squirrel, skydiving

7. High Resist

8. High Resist

9. Low Resist

10. Low Resist

11. Gravity Force that acts between any two masses
The greater the mass, the larger the gravitational force
The closer the objects, the larger the attraction
Acceleration due to Gravity = 9.8 m/s2

12. Gravity Factors Size/Mass Distance Bigger = more gravity
Ex: Jupiter, Earth, Moon
Distance
Farther = weaker

13. Gravity Free fall: Projectile Motion:
the motion of an object when only the force of gravity is acting on it
Projectile Motion:
The motion of a falling object after it is given initial forward velocity
Follows a curved path due to initial velocity and force of gravity

14. Weight and Mass Weight: the force of gravity acting on an object
Weight = Mass X Free-fall acceleration or w = mg (g = 9.8 m/s2)
Mass: measure of the inertia of an object; more mass = more inertia and weight

15. Gravity/Air Resist Gravity pulls down Air Resist. pushes up
Terminal Velocity = constant velocity when air resist is same as gravity
can’t go any faster

16. Mass & Weight Mass Weight Amount of matter Doesn’t change Balance
Unit = grams
Force of gravity
Changes (moon)
Scale
Unit = Newtons (N), Pounds (lb)

17. Earth’s Gravitational Acceleration
Equation: Force of Gravity =
Mass x accelaeration

18. Weight Weight = mass . gravity W = m . g
Units: W = N, m = kg, g = 9.8 m/s2

19. Projectile & Gravity
2 objects same time (no air resist) – will hit at same time
Even projectile & dropped object hit same time
Gravity only force pulling down

21. Centripetal Force Acceleration toward the center of a curved path.
Ex: The swings at a carnival
Swinging a bucket at the end of a
string.

22. 12.3 Newton’s 3rd Law of Motion
Whenever one object exerts a force on a second object, the 2nd object exerts an equal and opposite force on the 1st
Action – Reaction Force
The action/reaction force occurs at the same time; for every action, there is an equal and opposite reaction

23. Momentum The product of the objects mass and its velocity
The larger the mass, the more momentum
Equation:
Momentum = mass X velocity
Or: p = mv

24. Law of Conservation of Momentum
If no net force acts on a system, then the total momentum of the system does not change
In a closed system, the loss of momentum of one object equals the gain in momentum of another object