Unit 5

June 2010: Shinkansen in Osaka, Japan


Newtons three laws of motion explain the motion of something because something else moves it. These are just my interpretations of these laws; they probably aren't correct.

1. Every body remains in a state of constant velocity unless acted upon by an external unbalanced force.

Everything is always at a constant velocity, unless some force interferes.

As an example, this could mean that inside a car, you are moving at the same velocity as the car until the car breaks, then you get thrown forward (inertia?) because your velocity changes due to the cars change in velocity.

We did an experiment in seventh grade where we put a penny inside a balloon and shook it in a circle motion, and then stopped moving. If we did it fast enough, the penny would keep moving in a circular motion on the sides of the balloon.

2: A body of mass subject to a net force undergoes an acceleration that has the same direction as the force and a magnitude that is directly proportional to the force and inversely proportional to the mass, i.e., F = ma.

When something is pushed forward and accelerates, the mass is indirectly proportional to the force and proportional to the acceleration.

This one is really confusing and I don't really understand. So if a train is pushed forward from rest, the heavier it is, the less force it will take to keep it accelerating?

3: The mutual forces of action and reaction between two bodies are equal, and opposite (whenever a body exerts a force on a second body, the second body exerts a force on the first body. They are equal in magnitude and opposite in direction.

For every action, there is an equal and opposite reaction.

If I am facing my friend, and try to push her backward, and she is trying to push me forward, and we don't move, then our forces are equal. If I succeed in pushing her over, then my force was stronger.