NEWTONS LAWS OF MOTION

Sir Isaac Newton described all states of motion:
1. rest
2. constant motion
3. accelerated motion

1st Law of Motion: An object at rest will remain at rest and an object in motion will stay in motion (at a constant velocity) unless acted upon by an unbalanced force.

Example: A skateboard is at rest until an unbalanced force acts on it. (something moves it)
Example: A skateboard will continue to move until an unbalanced force acts on it.
(something stops it)

Inertia: the tendency for an object to remain at rest or to remain in motion

More massive objects have more inertia

QUESTIONS:

1. Which has more inertia: an empty or full shopping cart? Why?

2. Why do ships turn off thier engines miles from port?

3. When a car stops short, which way do you keep moving?

 

2nd Law of Motion: Force = Mass x Acceleration

The greater the force, the greater the acceleration.

Example: The harder you kick a ball, the faster it accelerates.

Questions:

1. Which takes a greater force, accelerating a small car 2 m/sec/sec or accelerating a large car 2 m/sec/sec? Why?

2. How much force is needed to accelerate a 1400 kg car 2 m/sec/sec?

3. What is the force of a 1000 kg elevator accelerating due to gravity?

4. A bowling ball is rolled with a force of 15 N and accelerates at 3 m/sec/sec. What is its mass?

3rd Law of Motion: For every action, there is an equal, but opposite reaction
(Action/Reaction Forces act in pairs)

ALL objects, even stationary ones like walls and floors, exert a force.

Example: Push down on the edge of your desk:
The mark indicates that the desk exerts a force.
The harder you push, the harder the desk pushes back.

Example: Rockets: gas is pushed out creating thrust.
As the gases push out, the rocket moves in the opposite direction.

Sample Problems:

1. Walking: How can you explain your motion using the 3rd law?

2. You are aan astronaut on a space walk and you use up all your jet pack fuel. How do you get back to the station?

Gravity: the force that causes objects to fall and accelerate toward the earth. It pulls equally and consistently on all objects.

Acceleration due to gravity = 9.8 m/sec/sec

An object's velocity is increasing 9.8 m/sec EVERY SECOND it falls.

Sample Questions:

1. An object dropped from a sky scraper has a velocity of 9.8 m/sec after one second. What is its velocity after two seconds? After three seconds?

2. If gravity pulls equally strong on all things, why will a rock hit the ground first if it is released at the same time as a piece of paper?

3. In a vacuum (no air resistance) which will land first, a rock or a feather? Why?

Newton's Law of Universal Gravitation: All objects in the universe attract due to the force of gravity.

Factors that affect the size of gravitational force:
1. the masses of two objects
(the greater the mass, the greater the force)

2. the distance between two objects
(the greater the distance, the smaller the force)