Body Systems: Cardiovascular System: Heart Squeeze

Get an idea how much force it takes to squeeze blood out of the heart....

The force needed to squeeze a tennis ball is similar to the force needed to squeeze blood out of the heart.

Gather enough tennis balls so you have one ball for every two students (if you can get one for every student, they activity will proceed a bit faster, as you won't have to repeat every step).  Ideally, you'll find someone who plays tennis and can get you as many dead balls as you could want - your phys. ed. teacher might be able to help you find someone.

If you have the time, and feel inspired, you can draw a heart on the balls, but it's by no means necessary.

Ask students to squeeze the ball as many times as they think the heart muscle squeezes in 15 seconds (they need to give the ball a good, solid squeeze).  Their partner can time them, or you (the teacher) can call out the time for the whole class.  Each student should record their squeezes.

Allow the partner students to repeat this step.

Now the students will squeeze the ball each time the teacher counts.  Call out one beat per second.  Go for a full minute if your students can handle it. 

Repeat for the other students.

Gather students feedback about squeezing the ball at the pace.  Their hands will be rather tired.

Now tell them that pace was for a person at rest, but no one stays that still when they are awake.

Go for another full minute, this time calling out beats faster than one per second.  You're aiming for about 80 counts in one minute. 

Repeat for the other students.