## Power, current, resistance Substituting Ohm’s Law, Tutoring physics with electricity

Amps and current were first thought of with Ben Franklin, so the convention is of positive charge moving.

Ohm’s law is useful when it’s applicable (which is likely throughout this class). V = IR

Power can be a variation of P = I V and power itself is energy divided by time. You can substitute Ohm’s law into that equation for variations.

Opposite charges attract, like charges repel.

Sometimes you will use things like kinematic equations with newer material.

## What is the Moment of Inertia?

We looked at rotational moment and the moment of inertial as well as some connected ideas.

The Greek letter omega stands for angular velocity, alpha stands for angular acceleration. Capital L stands for angular momentum. Capital T stands for the period.

Focused some time on algebraic manipulation of equations, especially with reciprocals and ways to simplify the equations.

It would help to write notes about what the teacher is saying for some problems rather than just what is on the board.

The ‘moment of inertia’, for which we use the capital letter I is basically how difficult it is to rotate something. Similar to mass in that it takes more force to accelerate a larger mass, it takes more torque to accelerate something in an angular way. It does not have to do with ‘a moment in time’.

## Car on Five Degree Incline with Friction, Energy Conversion

We started by looking at a problem with a car at the top of a five degree incline that rolled for 60 m. The force due to friction was given and the problem was to determine the velocity at the bottom of the incline and how far the car would roll given the same friction.

Energy can be converted to different forms. For this problem, there was gravitational potential energy at the top which was converted to kinetic energy. Along the path, energy was converted to heat (which is lost to motion) by friction.

## Tutoring Physics, Impulse & Change in Momentum

We looked at problems involving impulse and change in momentum. There were three forms of impulse that were all equivalent, you choose which one based on the information you have. Change in momentum, the sum of the forces multiplied by time or the impulse written with the letter J.

The problems we did involved finding the change in momentum.

In a different situation, you might know what force is applied and for how long.

The direction can be very important in calculations and can signify opposite directions.

## Tutoring Physics, Centripetal Acceleration

We looked at problems involving centripetal acceleration, movement in circular paths.

The new equation we used was that a(centripetal) = v^2/r

Looked at three problems. Also had to convert units a few times to SI units for the calculations to work.

One problem involved a person on a bike, another an object on a string, and the third an approximation of the Earth’s orbit as a circle in which we had to think about the period of rotation as being a year.

You can approximate the number of seconds in a year as being pi multiplied by 10^7. To be more accurate, you should account for leap year, making there be 365.25 days in a year.

## Tutoring Newtonian Physics, Day 1

We started by talking a little about what Newtonian physics is including what the units of force are and how you can break down Newtons in kg, s, and m.

Went into some problems include motion diagrams and plotting position vs time as well as velocity vs time.

Talked about normal forces and gravitational forces and how they often cancel when something is not moving vertically. And got into ‘resultant’ forces aka ‘net forces’ and how they can be zero for something at a constant velocity.

We also got into the differences between weight and mass and how kilograms compare to pounds. Thinking about the weight of a book, the weight of a person, etc.