DO WORK

Welcome to Unit 6, our last unit of the semester! We have done so much work in this semester that it seems right to end off the year with learning about

Work, Energy, and Power!

Work is defined as any change in energy (or the little triangle and a big E). To find variables while working with work, we use:

Work = Force x Distance

or W = F(d)

The units of work are Newton meters (Nm), otherwise known as Joules (J).

We also learned about the Law of Conservation of Energy which states that in an isolated system energy cannot be created nor destroyed, it just changes forms. Therefore, change(in) = change(out).

There are two kinds of energies:

Gravitational Potential Energy (PEg) - Energy of Position

Gravitational potential energy = mass x gravity x height

PEg = mgh

and...

Kinetic Energy (KE) - Energy of Motion

Kinetic energy = 1/2 x mass x velocity squared

KE = 1/2mv^2

The next thing we talked about was POWER. Power is the rate at which work is being done.

Power = change in energy/time

Power = work/time

The units of power are Joules/seconds, otherwise known as Watts.

When analyzing a force x distance graph, you should always remember: The area under the curve of a force x distance graph is WORK.

The last aspect of this unit that we covered so far was springs and elastic potential. The equation when dealing with springs is:

PEs = 1/2kd^2

where PEs is the elastic potential, k is the spring constant, and d is the distance stretched.

The bigger the spring constant, the harder it is to pull or stretch the spring. Therefore, with a larger spring constant, you need to apply more force.

When I was studying at Coffee Bean and Tea Leaf this afternoon, I accidentally dropped my pencil. I noticed that this was exactly like one of the problems that we discussed in class!

Let's say that my pencil with a mass of .4 kg fell to the floor from a table that was 2 m high. Can we find it's velocity?

Of course we can!

We first use the gravitational potential energy equation to find the amount of energy.

PEg = mgh

PEg = (0.2 kg)(10 m/s^2)(2 m)

PEg = 4 J

Then we use the kinetic energy equation to find the velocity.

KE = 1/2mv^2

4 J = 1/2 (0.5 kg)(v^2)

2 = (0.5 kg)(v^2)

1 = v^2

v = 1 m/s

Yay! We just did work!