31 . October Science 7 Big motion day–consolidating ideas, new phenomena, new concepts, getting ready for summative project #2

  1. Mindful moment
  2. Review DSN entry from last class (2 parts–WOW reflections, remembering and graphing the cart pulled with a constant force experiment)
  3. Preview today’s plan on today’s blogpost.
  4. Prepare DSN for today–everything in the motion folder.
  5. We will save questions for the end of class.
  • * * * *

Newton’s Laws of Motion

  1. All masses have inertia. Inertia is the tendency to for a mass to keep constant velocity (which could be 0 in some frames of reference). The constant velocity can be changed by an outside force.
  2. Forces cause masses to change their velocity. The change can be speeding up, slowing down, or changing direction. The change is proportional to the size of the force and the size of the mass. Bigger mass requires a greater force to achieve the same acceleration (remember dropping the clay balls of different mass). A greater force will cause a greater change in velocity in the same mass. Acceleration is comparing the change in velocity to the change in time. This is often written as F = ma.
  3. Forces come in pairs. For every force on an object there is an equal and opposite force pulling or pushing back. (The easiest way to begin understanding this is the experiment with two spring scales held by you and a partner. Neither of you can pull harder than the other. Both spring scales will read the same force but will be in opposite directions.

There are a few other aspects of motion that are part of the classical scientific understanding.

Velocity, Force, and Acceleration have direction. These are called vectors. We will look at two cases to help develop our understanding of why direction is important.

The concept of momentum is very important. For some it is almost intuitive. Momentum is defined as “mass times velocity.” Momentum can be transferred. Many students enjoy the “Newton’s cradle” toy. Momentum is also conserved.

Today:

  • We will do a simple demonstration experiment with an air pressure water rocket. Observe closely. Think of how all our ideas about motion apply.
  • We will spin the weight on a string and see which path it takes when released. This is a great demonstration of the consequences of Newton’s Laws.
  • We will look at a couple of “explosions” to begin developing our concepts of momentum and the conservation of momentum. This demonstration may also help with our explanation of the air-pressure water-rocket.
  • We will pull spring scales to see the simplest demonstration of Newton’s 3rd law.
  • We will look at the fan car and begin to decode the puzzle.
  • We will take questions.

Check out this video that ties together many ideas about motion–using momentum: https://www.youtube.com/watch?v=1-s8NZ8xKW0

This is an old but excellent video about momentum and collisions: https://www.youtube.com/watch?v=kn4TMxtQrwg

 

About rfrazier

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