To understand the difference between power and work. To convert the work done in horsepower.
- FILL BLANKS
When you are
climbing the stairs, you are doing work against the pull of ________ .
You gain potential ________ as your height increases and as your are
lifting your own _______. You burn your chemical energy (fator sugar) to do gain _________ energy.
work done (ENERGY spent) is equal to |force applied x distance| =
your _______ x height climbed with weight(N) = _____ (Kg) x
so WORK (J) = ________ (N) x ________ (m)If you climb the stairs running up or walking up you are doing the same _______________.
(because same weight, same height). However, You feel more tired if you run because:
THE RATE AT WHICH ENERGY IS TRANSFERRED IS GREATER.
THE RATE AT WHICH WORK IS DONE IS GREATER.
YOU ARE GETTING THE JOB DONE IN LESS ___________.
The rate at which work is done is called POWER noted P (rate here is energy produced per second) In the system international, work is in ________ (J) , time in _______ (s) and POWER in watts (W).
POWER (in watts) = WORK (in joules) / TIME (in seconds) or for short P = W / t
When you are climbing the stairs : WORK = WEIGHT x HEIGHT so
POWER = ___________________________ (use power = work / time with work = weight x height)
IF YOU RUN up the stairs instead of walking, you are PRODUCING MORE __________ eventhough the energy burn is the SAME.
the steam engine was first invented there was a need to describe the
rate a which the engine could work.
(how much energy burnt per second or how much coal burnt in 1 second)
Since people at that time were
familiar with using horses to do their work, the steam engines were
compared to _________.
James Watt, who designed a workable steam machine
engine, defined horsepower (hP) as a power rating of 550lbs ft/s.
That is horse can lift 550lbs , over a height of 1ft in one
People could then compare the new steam machines to the
familiar power of a horse:
An average horse can lift 550lbs over 1 foot in 1 second.
If you convert to joules you get a rate of 746 joules per second.
A horse produces _______ J per second or simply 746 watts. A horse power is a another unit for power.
1 horse power = 746 watts.
It is always fun to convert power to hp to compare your power
or the power of a machine to a __________
you need a bathroom scale, stairs case, meter stick, stop watch on line
USE A STAIR CASE. USE 2 floors.
of two students will measure the work done, the rate at which work is
done, and the horsepower rating as they move up a staircase.
will measure and record the data for person B. Person B will measure
and record the data for person A.
An ordinary bathroom scale can be
used to measure each person’s weight. Record the weight in pounds
(lb) in table 1.
This weight is the force (F) needed by each person to lift himself or herself up the stairs
The vertical height of the stairs can be found by measuring the height
of one step, then multiplying by the number of steps in the stairs.
Record the distanced d in feet (ft) in TABLE1.
( 1 foot = 12 in)
Step3: Measure and record the time required for each person to walk normally up the flight of stairs.
Record the time in seconds (s) in TABLE 1.
Calculate the work accomplished, power level developed, and horsepower
of each person while walking and while running up the flight of steps.
Be sure to include the correct units when recording the data in TABLE
|person A||person B||person C|
|weight (in pounds))|
|vertical height |
(in number of stairs)
|vertical height in feet|
(height of 1 stair x number of stairs)
|time (required in seconds)|
(weight in lbs x height in ft)
|Power = work (ft lbs) / time (s)|
|horse power = power / 550|
|how many horses in you ? |
convert last row number in fraction. use TI