Every day, millions of actions are being performed by you, me and everyone else in this world; aware actions, unaware actions, wanted actions, unwanted actions and many more. Every action performed costs energy. This energy is stored in our body and is obtained by eating certain food. Some actions are more common then others. For example: we walk every day, we write every day, we climb up and down stairs every day and many more. One thing younger people have to do every (school) day is lifting up their schoolbag to carry it on their shoulder…
The actions involved here are:
– the moving down of your arm towards the floor
– the getting hold of the bag itself
– the picking up of the schoolbag
– the rising of the schoolbag to shoulder height
– the moving of the one arm through the schoolbag-strap
The actual drawings of these actions can be found on page 3.
When these schoolbags get lifted up, it costs energy. However, these bags also gain energy; Potential Energy. The potential energy (Ep) is found b y multiplying the weight of the bag by the height that the bag is lifted up to. In letters:
Ep = (W) * H, or (M * G) * H (M)
W (weight, N) is the same as M (mass, Kg) * G (gravitational pull, N/Kg)
When we apply this formula to the situation with the schoolbags, and use average numbers for weight of school bag and height of student, this formula is obtained:
Ep = M * G * H
= 7.5(Kg) * 9.81 * 1.60(M)
= 73.575 * 1.60
= 118 (J) to 3 S.F.
The potential energy is equal to the work done because instead of multiplying the weight (or force) by the height, it is multiplied by the distance. Work:
W = F * D (or height)
W/Ep = F * H (or distance)
There are also different forms of energy in this simple and short (series of) action(s). The energy stored in our bodies is called chemical energy. When we perform an action, this chemical energy is converted to kinetic energy (the movement). When an object is lifted up, more chemical (body) energy is being burnt and converted into both kinetic and potential energy. However the potential energy is in the object itself.
In this situation, the schoolbag would contain the energy, so when we lift up the schoolbag, chemical energy (in our body) is converted into kinetic (moving) and potential (height) energy. Due to friction, however, some energy is lost. This friction can be air resistance and is lost as heat or sound. In other words, some of the energy used is not used as useful energy, due to friction.
When this action is related to the areas of interaction, the most likely area of interaction would be health and social education. There are thousands, if not millions, of people with back problems. There are many reasons for this but one main reason is that they have carried too heavy objects, for too long a time. It has become a serious problem, reaching media in the forms of radio, TV and newspapers, and many medically related people are alarmed by the many kilos of books students have to carry to school and back home every (school) day.
Another aspect of health would be that any action performed, no matter what it is, burns energy. Things like sleeping, typing on a computer and moving your eyes around to see what’s going on. From the littlest thing to the most impossible exhausting exercise, it all burns energy. This energy does not last forever, but if we eat enough healthy and ‘energy-containing’ food (carbohydrates), we can replace the used up energy by new, fresh chemical energy.
In conclusion, it can be said that every single thing we do, or think of, burns some (or lots of) energy from our chemical energy storage inside our bodies. Lifting up a schoolbag costs 118 (J) of energy every time it is lifted, which happens several times a day. We can get very tired of this and we can even get tired from just moving around with our schoolbag on our shoulders. This is because every movement we make we do burn some energy, which does not last forever.
From this project I have learned that we burn at least some energy in everything we do and that we must eat a healthy diet that gives you enough energy to last another day.
The reason I chose this action is that I find my schoolbag far too heavy sometimes. This is mainly due to the fact that we have loads of homework, and all these huge books we need for every class. A possible solution might be that we get less homework and don’t have to bring those big, heavy books to class…
If we lift up our schoolbag on average 10 times a day, that will result in
10 * 118 (J) = 1180 (J) When this result is compared to swimming (which has an energy transfer rate of 500 J/s)
then lifting up our schoolbag to our shoulders burns just as much energy as
nearly 2.4 seconds of swimming. 500 * 2.4 = 1200 (J).
An apple is 400 (KJ), or 400000 (J). This is equal to the energy burnt when
we lift up our schoolbag 3390 times (nearest whole number) after using the equation:
400000 (J) / 118 (J/bag lifting) = 3389.83 times lifting.
So when we lift up a schoolbag 3390 times, we have burnt the energy in 1 apple.
All in all, we take in loads of energy, and we burn loads of energy: Keep it balanced!!!
Note: in the above essay, friction is ignored.