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2. The Law of Conservation of Mass
The Law of Conservation of Matter (or Mass) states
that matter cannot be created nor destroyed in an
ordinary chemical reaction. No atoms are gained or
lost in a reaction; they are just rearranged.
The total mass of reactants = Total mass of
products

3. Work
Work is the transfer of energy through motion. In
order for work to take place, a force must be exerted
through a distance.
The amount of work done depends on two things:
The amount of force exerted
The distance over which the force is applied.
Direction of movement
as result of Force
Direction of Force
Object

4. Work
 If you push a box with a force of one Newton for
a distance of one meter, you have done exactly
one joule of work.

5. Work (force is parallel to distance)
Force (N)
Work (joules) W=Fxd
Distance (m)

6. Work (force at angle to distance)
Force (N)
Work (joules) W = F d cos  Angle
Distance (m)

7. Work done against gravity
Mass (g)
Height object
Work (joules) raised (m)
W = mgh
Gravity (m/sec2)

8. Power
 Power is defined as the rate at which work is done. It
can also refer to the rate at which energy is expended or
absorbed.
 Power is equal to the amount of work done
divided by the time it takes to do the work.
Power (W) Change in work
or energy (J)
P = E
t
Change in time (sec)

9. Power
A unit of power is called a watt.
Another unit horsepower.
One horsepower (the avg
power output of a horse) is
equal to 746 watts.

10. Power
Another way to express power is as a multiple of
force and it's velocity, if the velocity and force are
both vectors in the same direction.
Power (W) P=F.v
Velocity (m/sec)
Force (N)

11. Efficiency
 Efficiency can also mean the ratio of energy output
divided by energy input.
Energy output (J)
Efficiency Eo
e=
Ei
Energy input (J)
Wout work done with no friction (often m g h)
eff = = work actually done by input force
Win
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12. Efficiency
 Efficiency is defined for a
process.
 A process is any activity
that changes things and
can be described in terms
of input and output.
 The efficiency of a process
is the ratio of output to
input.
Efficiency – 10%

13. Energy flow in systems
Energy flows almost always involve energy conversions.
To understand an energy flow:
1. Write down the forms that the energy takes.
2. Diagram the flow of energy from start to finish for all
the important processes that take place in the system.
3. Try to estimate how much energy is involved and what
are the efficiencies of each energy conversion.

14. Energy flow in human technology
The energy flow in technology can usually be broken down
into four types of processes:
1. Storage ex. batteries, springs, height,
pressure
2. Conversion ex. a pump converting
mechanical energy to fluid energy
3. Transmission ex. through wires, tubes,
gears, levers
4. Output ex. heat, light, electricity

15. Energy flow
 The energy flow diagram
for a rechargeable electric
drill shows losses to heat
or friction at each step.

16. Energy flow

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