1. Chapter 3—Forces

2. Section 1: Newton’s Second Law
For any object, the greater the force that’s applied, the greater its acceleration will be
Force and Mass: Acceleration of an object depends on its mass as well as the force exerted on it
Force, mass and acceleration are connected

3. Newton’s Second Law
Describes how force, mass and acceleration are connected
Net force acting on an object causes the object to accelerate in the direction of the force
OR: acceleration = net force / mass
OR: Force = mass X acceleration

4. Friction Objects slow to a stop when moving freely—due to friction
The force that opposes motion between two surfaces that are touching ea/other
Amt. of friction depends on kinds of surfaces and the force pressing the surfaces together

5. Types of Friction:
Static Friction: friction between two surfaces that are not moving past ea/other
Sliding friction: force that opposes the motion of two surfaces sliding past ea/other
Rolling friction: friction between a rolling object and the surface it rolls on

6. Air Resistance:
The force on an object opposite the force of gravity when an object falls toward Earth
Effects anything that moves in Earth’s atmosphere
The amount of air resistance on an object depends on the speed, size and shape of the object

7. Terminal Velocity
The highest velocity that a falling object will reach
As an object falls, it accelerates and its speed increases
The force of air resistance increases until it becomes large enough to cancel the force of gravity
(How sky divers can land softly)/video clip

8. Section 2--Gravity
Law of Gravitation: any two masses exert an attractive force on ea/other
The attractive force depends on the mass of the two objects and the distance between them
Four Basic Forces:
*Gravity *Strong Nuclear *Electromagnetic
*Weak Nuclear

9. 9.8 m/s/s
Near Earth, the gravitational attraction of Earth causes all falling objects to have an acceleration of 9.8 m/s/s
SO: F = Mass X 9.8 m/s/s
The force of the Earth’s gravity is always downward
When an object is influenced only by gravity—free fall

10. (more on Gravity)
All objects fall w/the same acceleration, no matter how large or small their mass
Weight: actually the gravitational force exerted on an object
Gravitational Force = Mass X Acceleration due to gravity

11. SO: Weight = mass X 9.8 m/s/s
Greater mass means greater gravitational force, means greater weight
Projectile Motion: anything thrown or shot through the air is said to be in projectile motion
Projectiles follow a curved path-due to inertia

12. Horizontal and Vertical Motions
Centripetal Acceleration: acceleration toward the center of a curved or circular path
Centripetal force: an unbalanced force, accelerating an object toward the center, exerted by the outside wall pushing against it and keeping it from going straight

13. Section 3: Newton’s Third Law
Describes action/reaction pairs
When one object exerts a force on a second object, the second one exerts a force on the first that is equal in size and opposite in direction
OR: “to every action force there is an equal opposite reaction force”

14. Remember: Action/Reaction forces are acting on different objects
Even though forces are equal, they are not balanced

15. Rocket Propulsion
Rockets use the principle that as the rocket exerts force on gases and causes them to escape out the back of the rocket, the gases exert an opposite but equal force on the rocket propelling it forward

16. Momentum
Related to how much force is needed to change an objects motion
Momentum of an object is the product of its mass and velocity (abbrev is P)
OR: P = Mass X Velocity
Units used to report momentum are as follows: Kg m/s

17. Law of Conservation of Momentum
Momentum of an object doesn’t change unless its mass, velocity or both change
Momentum, however, can be transferred from one object to another
Momentum is not lost or created, only transferred from one object to another