Physics 2.3: MS & Upper Elementary

 Hello Everyone,

Well, today's topics were power, energy loss and friction.  Believe it or not, I did not throw any balls at anyone.  I did get pushed around while standing on a book, though, so I guess this time I was the one taking the abuse*.  Power is the amount of work done in a given amount of time.  We related that to electricity, talked about light bulbs and how they change electrical energy into light energy + heat.  We talked about energy "loss" (energy is not destroyed, but it changes form into something that is no longer useful) and then discussed friction.  Friction is a force that opposes motion and it causes energy "losses" in every system in the real world.  We don't want a world without friction, however, because then we wouldn't be able to walk or move even (compare walking on the floor vs. walking on ice).  The force of friction depends on three things: (1) the roughness of the surfaces interacting, (2) the force between the two surfaces, and (3) whether the object is at rest (static friction) or moving (kinetic friction).  

We didn't do an experiment today, but instead did an activity where the kids tried to measure how much power they exerted when running up a flight of stairs.  They should have a handout that explains the activity and how to calculate the power they exerted.  One thing to note is that we measured their weight in lbs, not in kilograms, so your child will need to convert from lbs to kg (just divide the weight in lbs. by 2.2 to get kgs).  There are some discussion questions to answer on the sheet--this is required for the Middle schoolers but optional for the Upper Elementary.  The rest of the homework is on the backside of the sheet and up on the website too ( https://memorialcoopstl.blogspot.com/p/23.html).

Alright, this was my last class with your wonderful kids--it's been neat to see them engaging with the material.  Thanks for letting me teach them!

Sincerely,

-Liz

*In case you're wondering the context: I was trying to show that one of the factors that affects the amount of friction between two surfaces is the amount of force acting between the two surfaces.  So, the frictional force from pushing a book is not too high because the weight of the book is the only force acting on the interface between the book and the ground, but if I stand on the book, the frictional force is much higher because my weight plus the weight of the book is the force acting on the interface between the book and the ground.