Section 2-1 chapter 2
I. What is force?
a. Force is a push or pull
b. A force causes an object to start moving, stop moving or change its direction
II. Combining forces
a. Two forces in the same direction get added.
b. Two forces in different directions subtract
c. When the total force is in one direction, it is called an unbalanced force
d. If 1 direction is greater, the object will move in the direction of the greater force.
e. Forces in opposite direction and equal force are called a balanced force
f. In a balanced force in opposite directions, there is no movement
Section 2-2 Chapter 2
I. Friction: A force opposing motion
a. Whenever 2 forces touch, there is friction
b. Friction will cause an object to slow down and finally stop
c. The amount of friction depends on how hard the surface is and the material that the object is made of.
d. Friction moves in the opposite direction of the force that is applied
e. Sliding friction – when objects slide over each other
f. Rolling friction – objects that have wheels
g. Fluid friction – friction caused by fluids such as water or air
- You reduce friction by adding a lubricant such as oil. You can never get rid of friction all together.
Section 2-3 Chapter 2 – Newton’s Law of motion
I. Newton’s 1st law
a. Friction brings an object to rest
b. If there was no friction an object would travel forever
c. A tendency for an object to stay at rest or in motion is called inertia
d. 1st law states that all objects will stay at rest or an object in motion will stay in motion unless acted upon by an unbalanced force.
e. There is acceleration only in the presence of a force.
II. Newton’s second law
a. Force mass and acceleration are related
b. Force =Mass x Acceleration
c. Force can be written as kg-m/sec/sec or Newtons (N)
III. Newton’s 3rd Law
a. For every action there is an equal and opposite reaction. Ex. – rocket, walking
b. 1st law shows that a force is necessary to change motion, 2nd law says how mass, acceleration and force are related, 3rd law explain how forces work in pairs
Section 2-4 Gravity
I. Falling Objects
a. Acceleration of a falling object due to the pull of gravity between object and the earth
b. Acceleration rate is 9.8 m/sec/sec
II. Air Resistance
a. Any falling objects meet air resistance
b. As objects fall, air resistance equals the pull of gravity
c. When forces are balanced there is no acceleration
d. When falling objects no longer accelerate, the hit terminal velocity
III. Newton’s Law of Universal Gravitation
a. All objects in the universe attract each other by the force of gravity
b. The pull of gravity depends on the mass of the object and the distance between them
c. Gravity holds us to the earth and holds the planets in orbit
IV. Weight and Mass
a. Weight is the measure of the pull of gravity
b. Your mass is the same anywhere on earth or anywhere in the universe only weight can change
c. Weight changes the further from the center of the earth you are.
d. Weight = Mass x acceleration due to gravity w= m x g.
- Unit of weight is the newton the unit for weight is grams.