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9
Learning About the Muscular System and
Work
There are about 600 muscles in your body that make up 40% of
your weight. Muscles have many functions. For example, they
keep your heart beating, pull your mouth into a smile and move
the bones of your skeleton.
Muscles fall into three categories: cardiac, smooth, and
skeletal muscles. Cardiac muscles are only found in the heart and
make up the heart’s tissue. Smooth muscles make up the walls of
hollow organs in the digestive, circulatory, respiratory, and
reproductive systems. Skeletal muscles are attached to bones and
help your body move.
Remember, bones are connected to muscles by tendons.
Muscles move only in one direction –they pull bones together.
They cannot push bones apart. Muscles that move bones work in
pairs. One muscle contracts and pulls the bones together. This
type of muscle is called a flexor muscle. This causes the second
muscle to relax. Then the other muscle contracts and pulls the
same bones apart causing the first muscle to relax. We call this
muscle an extensor muscle.
Observe the picture and answer the
5 questions.
1. Name the two muscles in the
picture._____________________
2. Which muscle is contracting
when you bend your arm and is the
flexor muscle? ____________
3. Which muscle is relaxing when
you bend your arm and is the
extensor muscle? _____________
4. Which muscle is contracting when you straighten your
arm? _________________________
5. Which muscle is relaxing when you straighten your
arm?___________________________
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Activity 1
Materials: student partner
What To Do:
1. Sit in your chair and place you hand on the top of your head.
2. Your lab partner will try to pull your hand off your head.
3. Your partner can only use one hand and must lift straight up.
Don’t pull to the side, and no jerking allowed!
4. You must try to keep your hand from leaving your head.
Questions:
1. Which muscle are you contracting? _____________
2. Which muscle is relaxing? ___________________
3. Which muscle is your lab partner contracting during this
activity? ________________
4. Which muscle is your lab partner relaxing during this
activity? _________________
5. Which muscle appears to be stronger? ___________
Activity 2
Materials: spring-type clothespin, timer
What To Do:
1. Grip the clothespin with the thumb and index finger of your
writing hand.
2. Squeeze the clothespin open and shut as quickly as possible
for 30 seconds. Your partner will use the timer to time you.
Count how many times you can squeeze .
4. Rest for 10 seconds and repeat.
5. Complete 4 trials.
6. Record your information and repeat with your partner.
Names
Trial 1
Trial 2
Trial 3
Trial 4
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Questions:
1. What happened to your muscles as you continued the
trials? ______________________________________
2. Why do you think this happened? ______________
____________________________________________
3. You had to use force to open the clothespin. Where did
the force come from? _________________________
Activity 3 – To Think or Not To Think
The heart and diaphragm are both muscles we have no
control over. These types of muscles are called involuntary
muscles, meaning that they work automatically. Moving
them does not involve any thought. Muscles that we control
are called voluntary muscles, meaning that the muscles
work because you tell them to.
Read the procedures below and complete the following data table
and questions.
Action
Pupils of Eyes
Knee Jerk
Blinking
Action
Pupils of
eyes
Knee jerk
Blinking
Procedure
Partner 1: Stare at a fixed point in the classroom
Partner 2: Shine the flashlight into partner 1’s eye
from the side of the face (not directly from the
front). Next, turn off the flashlight. Observe partner
1’s pupils.
Partner 2: Sit on the edge of the table and relax
both legs.
Partner 1: Make a fist and LIGHTLY hit just below
your partner’s patella.
Partner 1: Put on the safety goggles and relax.
Partner 2: Throw the cotton ball at your partners
eyes.
Vuluntary
Muscle?
Involuntary
Muscle?
Why is it involuntary or
voluntary?
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Questions:
1. Is breathing voluntary or involuntary? Why? ____________
__________________________________________________
2. What are the main functions of the muscular system?
__________________________________________________
__________________________________________________
__________________________________________________
Your muscles and Work
You and your friends use your muscles to try to push a car out
of the ditch. After 10 minutes of pushing really hard, you’re
muscles are very tired. The car is still stuck in the ditch. That
sure was hard work, wasn’t it? You exerted a lot of force. But
you might be surprised to discover that, in scientific terms, you
didn’t do any work at all on the car!
In science you do work on an object when you exert a force
on the object that sets the object into motion. So why didn’t you
do work in trying to push the car out of the ditch? The car didn’t
move. In order for you to do work on an object, the object must
move some distance as a result of your force.
The amount of work you do on any object can be calculated.
It depends on both the amount of force you exert (measured in
Newtons) and the distance the object moves (measured in
meters). So you can calculate the amount of work done on an
object by multiplying force times distance. The (SI) unit for
work is a Newton meter (Nm) and that has been name Joules (J)
for James Prescott Joule.
Work = Force X Distance
If you exert a force of 20 N on a table to move it
10 m, how much work do you do?
_________ X __________ = __________
force
distance
work
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DO NOT GLUE
DO NOT GLUE
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Name _______________
period _____
EXIT TICKET
Muscles and Work
1. What is the function of the muscular system?
A. To bring air into the body
B. To take blood around the body
C. To move your bones
D. To control your responses
2. What is an example of an involuntary muscle?
A. heart
C. biceps
B. triceps
D. brain
3. Muscles we have control over are called –
A. cardiac muscles
B. voluntary muscles
C. involuntary muscles
D. smooth muscles
4. A box weights 3000N and you wanted to move it
10m but you could not get it to move. How much work did you do?
a. 3000 J
b. none
c. 30,000J
d. 300 J
5. What is the formula for calculating Work?
a. weight x distance
b. work x distance
c. force x distance
d. mass x distance
6. If you move a 10N box 5m, how much work have you done?
Show your work.
Teacher instructions
Show students video clip at the following website
http://glencoe.mcgrawhill.com/sites/0078778360/student_view0/chapter4/conce
pt_animations.html#
Have students make page 13 a foldable. Cut on the dotted
lines and fold on the solid line. Have them glue only the
thin area between the dotted line and the solid line in their
notebook.
Under each flap have the students copy and answer the
following questions:
1. What is the force used on the box? ____________
2. What is the distance the box was moved? ________
3. Calculate the work done on the box. Show your work!
If time allows, watch the Muscles video from
www.Brainpop.com