Energy-Work-Power

In class this week, we talked about energy, work, and power. Energy is a scalar quantity, which means that it is only measure with magnitude, no direction. Energy is also conserved in an isolated system, which means that total E_in=E_out. Energy can be potential (energy of position), which can be expressed with the equation PE=(mass)(gravity)(height). Energy can also be kinetic (energy of motion), which is expressed with the equation KE=1/2(mass)(velocity) ². The unit of energy is Joules. Work is a change in energy, and can be written as W=(force)(distance). The units of work are Newton meters (Nm) or Joule (J). Power is the rate at which work is being done. Power can be written as P=∆Energy/∆Time. The units of Power are Joules/Second or Watts.

When I think of potential and kinetic energy, I think of something falling from a height. The picture below is of me jumping off my bed.

Knowing that my mass is 60kg, and gravity’s pull is 10m/s², and assuming my bed is 0.5m high, I can find my potential energy standing on my bed.

PE=mgh

PE=(60kg)(10m/s²)(0.5m)

PE=300 J

Using my mass, and assuming that when I fell I reached a velocity of 3.16m/s, I can find my kinetic energy right before I landed.

KE=1/2mv²

KE=1/2(60kg)(3.16m/s) ²

KE= 300 J

Physics is boiz

I am super thankful for physics and everything it has taught me so far. Out of all the things I have learned in physics so far, one thing that I am most thankful for is that awesome thing called gravity. Without gravity’s force of 9.8m/s² down accelerating on us all the time, we would all just float away into space. Another thing I am thankful for in the world of physics is kinematics and motion. Kinematics is the study of forces that cause motion, and motion is a change in position over time. Without motion, life would literally be standing still. I am super thankful that I can move. The picture below is a perfect example of why I love gravity and motion. One of my favorite feelings in the world is falling. This is because our bodies only feel acceleration not constant velocity, and the acceleration you feel when falling is gravity. Falling wouldn’t be possible without motion either, which is why falling is a great example of gravity and motion.

Momentum

In class this week, we have been talking about momentum. Momentum is the quantity of motion of a moving body. Momentum is equal to mass times velocity, and can be expressed in the equation, P(momentum)=M(mass) x V(velocity). This means that objects with more mass and more velocity have more momentum. Another thing we have been talking about in class is Impulse, which is equal to change in momentum. In the picture below there is a key and a pencil. Assuming someone threw both at you at the same velocity, the key would hurt more because it has more mass, which means more momentum.

If the key weighs .5kg, and the pencil weighs .2kg, and both are thrown at a velocity of 2m/s, we can calculate the momentum of both objects.

P_key=M_keyV_key

P_key=(.5kg)(2m/s)

P_key=1kg m/s

P_pen=M_penV_pen

P_pen=(.2kg)(2m/s)

P_pen=0.4kg m/s

The key has a momentum of .6kg m/s greater than the pencil.

Forces that Accelerate

This past week in physics we have been talking about Newton’s Laws of Motion. Newton’s 2^nd Law of motion that states that acceleration is directly proportional to the net force of an object, and that acceleration is inversely proportional to the mass of an object. This is easier to explain with the equation Fnet=ma, where Fnet is the sum of all forces, m is mass, and a is acceleration. This can also be written as a=Fnet/m. This equation can be used to find the total force, mass, or acceleration of many situations according to what is given. The picture below is my foot kicking my skateboard that is rolling at me. Another one of Newton’s Laws states that for every action there is an equal and opposite reaction, equal in magnitude and opposite in direction. This means that the total force (Fnet) of my foot hitting my board and my board hitting my foot is equal.

Assuming that my foot has a greater acceleration than my board, I can find out that my board has a greater mass than my foot.

Fnet_foot=Fnet_board

ma_foot=ma_board

(smaller mass)(bigger acceleration)=(bigger mass)(smaller acceleration)

equal and opposite forces