Energy Review

What is energy? Class Discussion: When do we use energy? What are some types of energy? Think Pair Share: Can you save energy? Definition: –Energy is the ability to cause change.

Law of Conservation of Energy Remember, a scientific “law” is a statement about how things work in nature that seems to be true consistently. (like gravity, laws are almost never changed nor argued unlike theories) Says that energy can be transformed from one form to another, but it cannot be created or destroyed.

Example of this law… Flash Light Energy is stored into a battery as chemical energy When you turn on the flashlight, the chemical energy is transformed into radiant and heat energy. The amount of energy that the flashlight gives off (in heat and radiation), cannot be greater than the amount of chemical energy stored in the battery.

Energy Transfer Occurs when energy moves from one object to another without changing form. –Example…. Kicking a ball (your foot is in motion with kinetic energy and that energy is transferred to the ball giving it kinetic energy)

Energy Transformation When one form of energy is transformed into another form of energy –Chemical energy transformed to radiant and heat in a flashlight –Chemical energy in your legs muscle that transforms to kinetic as you walk. –Kinetic wind energy transformed into electricity

What is a Force? Force is calculated in Newtons. –1 newton is equal to the amount of energy it takes to accelerate a one kilogram object one meter per second squared –F = ma (F-Force, m-mass, a-acceleration)

Let’s Try it! Mattel wants their new 4kg toy car to accelerate at 12 meters per second squared. What is the force required? –F=ma –F= 4kg x 12ms 2 –F=48N

Energy and Work Work is the transfer of energy that occurs when a force makes an object move in the direction of the force. –Shoving a box across the floor –Running the half mile in PE The equation for work is W = F x d –W = Work (measured in joules) –F = Force (measured in newtons) –D = Distance (measured in meters)

Let’s try it out A student slides a library book across a table. The student pushed the book with a force of 8.5 N (newtons) and a distance of 0.3 m (meters) –W=F X d –W= 8.5N x 0.3m –W= 2.55J

Here we go again… A student lifts a backpack straight up with a force of 53.5 N for a distance of 0.65 m. How much work is done on that backpack? –W=Fxd –W = 53.5N x 0.65m W = J –Can you round this?

What is Power? Power is the amount of work done divided by the amount of time it takes Power is measured in Watts (W) –1 Watt is equal to 1Joule per 1Second

So what does this mean? If you do lots of work, but it takes you a long time, you have little power. If you do only a small amount of work in a small amount of time, you have little power. If you do lots of work in a short amount of time…..

Your math teacher will be happy… Jacob is running stairs. He is using 72.4 newtons. It takes him 5.6 seconds. What is his Power? –P = F/t –P = 72.4 / 5.6 –P = 12.93