Chapter 7, 8, & 9 by Devabhadra Haridas

CHAPTERS 7, 8, & 9

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Chapter Seven - Energy

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energy

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Chapter seven of the textbook mainly focuses on energy. Energy is the ability of things to change themselves or to cause change in other things. It's defined as the ability to do work.

A few of the changes are changes in temperature, speed, position, pressure or any other physical variable. It also causes change in material sometimes.

work formula:

WORK= force*distance

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Energy is the ability to do work, work is the transfer of energy that results from applying a force over a distance.

when you work the equation for work, always be clear about which force is acting on the object.

example:

When you lift a box you're doing work, to find how much work you did you multiply the distance you picked it up and the force you used to pick it up.

In this case, say you picked it up with 1 newton of force and lifted it 1 meter

Forms Of Energy:

mechanical: a form of energy that is related to motion of position.

Potential and kinetic are examples.

chemical: a form of potential energy that is stored in molecules.

electrical: comes from electrical charge

pressure: pressure in gasses and water have energy too.

nuclear: a form of energy that is stored in the nuclei of atoms.

radiant: a form of energy that is represented by the electromagnetic spectrum.

potential: energy due to position.

kinetic: energy of motion.

POTENTIAL ENERGY FORMULA:

E(p)= mass*g(9.8m/s/s)*height

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example:

if there is a block that has a mass of 1 kg and is 1 meter above the ground you would take the values and multiply.

1 kg* g(9.8m/s/s)* 1 meter= 9.8 j

KINETIC ENERGY FORMULA:

E(k)= 1/2mass*velocity^2

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example:

you have a block that has a mass of 1 kg and its traveling at a speed of 10 m/s

1/2*1kg*10 m/s ^2

= 50 j

Energy is always being used by us everyday. Will we ever run out? No, because energy cannot be created of destroyed only transformed to another form.
The law of conservation of energy states that energy can never be created or destroyed, only transformed into another form, the total amount of energy in the universe is constant
Energy conservation is a direct way to find out what happens before and after a change from one form of energy to another.
Applying energy conservation allows you to find speeds and heights easily.

Like when you "use "energy in an everyday sense, for example, when you turn on a light, you really are converting it from one form to another.
Electrical plants don't create energy, they just convert it.

joule

idevah88 — 2017-11-12 16:32:07 UTC

A joule is a measurement of energy.

1 joule = 1 newton- meter

1 newton = 1kg*m/s

so.. 1 joule = 1 kg*m/s

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a 100 watt light-bulb uses a 100 joules.

the sun

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Earth's main source of energy is the sun.

it gives energy to every living thing on earth.

Chapter 8 - Work

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Work

idevah88 — 2017-11-12 17:10:35 UTC

Work is a form of energy that comes from a force applied over a distance. A force of1 newton does 1 joule of work when the force causes 1 meter of motion in the direction of the force.
without energy work is impossible
The path of a force does not matter because work is only done by the part of a force that acts in the direction of the motion

Work Formula:
Work = force* distance (in direction of the force)
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example:
You apply a force of 5 newtons on an object, and it moves 5 meters in the direction you push it.
5 N* 5 meter= 25 joules
** if you apply a force and the object doesn't move, you have not done any work.

Work done against gravity is equal to weight multiplied by change in height.

Efficiency and Power
Every process that transforms energy can be considered a machine. Work or energy goes in one end and work or energy comes out the other. That "machine" may be a toaster heating up bread or a human being consuming food.
work input is the work that is done on an object
work input is the work that an object does as a result of work input.
The energy output of a machine can never exceed the energy input.
Work output is always less than the work input because some work is always converted to heat and other kinds of energy by friction.
Efficiency is the ratio of usable output work divided by the input work. Efficiency is often expressed as a percent, with a perfect machine having a 100 percent efficiency.

power is the rate of doing work or moving energy.Power is equal to energy(or work) divided by time.
units:
watt(W) is a unit of power equal to 1 joule per second.
horsepower(hp) a unit of power equal to 746 watts. or 746 joules per second.

power= work / time
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if you lifted a barbell using a force of 5 joules in 10 seconds you you power is 1/2 of someone who lifts in 5 seconds

5/10= 0.5
5/5=1

III - levers in the human body

idevah88 — 2017-11-12 17:11:55 UTC

the human body contains levers just like a machine! that's because it is a machine. your arms and legs are all levers. your joints can be considered fulcrums

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Chapter 9- Simple Machines

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idevah88 — 2017-11-12 20:58:06 UTC

Using machines
A machine is a device with moving parts that work together to accomplish a task.
Input is forces, energy, or power supplied to make a machine accomplish a task.
Output is forces, energy, or power provided by the machine.
for example, work input is applied to pedals on a bicycle, work output in that situation would be the forwards motion of the bicycle.

A simple machine is an un-powered mechanical device that accomplishes a task with only one movement.
A lever is a stiff structure that rotates around a fixed point called a fulcrum.
A gear is a rotating wheel with teeth that receives or transfers motion and forces to other gears or objects.
other simple machines include: a ramp or inclined plane, wheel and axle, a wedge, and screw.
A simple machine has no source of energy except for the immediate forces applied to it.
The output is always less than the input.

Mechanical Advantage
mechanical advantage is the ratio of output force to input force.

If the mechanical advantage is...
>1 then output force is >1
<1 then output force is <1
=1 then the output force is =1

Mechanical Advantage Formula:
MA= F(output in N)/F(input in N)
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example:
output:2 input:3
2/3= 0.67

Lever
A lever is a stiff structure that rotates around a fixed point called a fulcrum
The length of the lever arm is indirectly related to the corresponding force.
Mechanical advantage can also be calculated by dividing the length of the input arm by the length of the output arm

Gears
Gears can transfer motion and force when the teeth of one gear press on the

teeth of another gear as each gear rotates around a shaft

-gear multiply forces
load is the amount of force or weight that a machine lifts or moves.
gear ratio is the ratio of output turns to input turns for a pair of gears.
force is multiplied when the input gear is smaller and has fewer and has less teeth. speed is increased when the input gear is bigger.
Gear Ratio Formula:
(turns of output gear) T(o) (number of teeth on input) N(i)
(turns of input gear) T(i) (number of teeth on output) N(o)
T(o)/T(i)= N(i)/N(o)
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Rope and Pulley Systems
Ropes and strings carry tension forces along their length. tension is the same at every point of a rope

ropes and string do not carry tension forces
the mechanical advantage of a pulley system depends on the number of strands of rope directly supporting the load.

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idevah88 — 2017-11-14 20:15:19 UTC

The joule is a tiny amount of energy compared to what you use everyday.
other units of energy are:
the kilowatt-hour (kWh)
food calorie
and the British thermal unit (Btu)