In 1483 Leonardo Da Vinci wrote that,

"If a man is provided with a length of gummed linen cloth with a length of 12 yards on each side and 12 yards high, he can jump from any great height whatsoever without injury."

That was a rather bold statement in that time period, and it took more than three hundred years before anyone performed a successful parachute jump (1797)¹. The design was a bit different than the one shown in the Da Vinci sketch, but the principles involved were the same (Leonardo's design was proven viable more than 500 years after his sketch was done²). Let's take a closer look at the principles behind the parachute.

First, a question: Why do we use a parachute when jumping from a high altitude? One answer is obvious - the parachutist wants to be moving slowly so that he/she can land with no problems! From a physics standpoint, the goal is to oppose the force of gravity which is acting downward on you with a constant force. Thus, the goal of the parachute is to oppose the gravitational force, and this is done by a drag force which acts upward.

In simple terms, a drag force is a force that created when trying to move
one object through another dense medium. You can feel a real world example of this by moving your hand through water (such as a filled sink or swimming pool). When your hand is motionless in the water do you feel any forces acting on your hand? When you move your hand to the right do you feel a force? What about the left? While moving your hand to the right you should feel a force trying to oppose your motion (which is why it is much easier to move your hand through the air than through water). When moving your hand to the left does the force acting on your hand change direction?

The drag force tends to always oppose the direction of motion so when something is falling downward through the sky the drag force acts upward.

Think about one more thing: suppose you have a balloon with no air inside it and you drop it. Then fill the balloon with air and drop it again. Did the same balloon fall at two different rates? Why do two objects of the same mass (approximately) drop at different rates? The difference between the two is that one has a greater volume, and since density = mass per unit volume the objects have a different density.

With the Freefall Lab we can study how things behave as they are falling
(or even bouncing). The main features of the lab are shown in the
following diagram.

This Gizmo represents a laboratory situation in which a sonic ranger (a device which measures distance at specific time intervals) is placed at a certain distance above the ground and objects can be studied as they are falling beneath the sonic ranger.

Freefall Lab

In this activity there are many possible teaching opportunities. We'll walk through one aspect this month and discuss another next month.

Notice that there are many variables that can be changed in this simulation. Set the radius of the ball to 0.02 meters, the mass to 0.25 kilograms. Leave all
other parameters at the default values. Release the ball. Measure the acceleration at the start of the fall and the end of the fall (acceleration is indicated by the green dots, velocity by the blue dots, and position by the red dots). Placing the cursor over the graph region provides feedback on the current x and y values just below the graph.

Find the average acceleration during the drop.

Since this is a relatively heavy object with a small radius the acceleration should be approximately 9.8 m/s2. Was this the case. If not, there might be a small bit of systematic error in the sonic ranger. Keep this in mind for future readings.

Reduce the mass of the ball several times and continue to find the average acceleration (it is sometimes helpful to use the 'Clear Trails' button between releases). Suggested values are 0.15 kg, 0.10 kg, 0.05 kg, and 0.01 kg. Is the average acceleration changing as the mass changes?

Make a plot of average acceleration vs. the density of the falling object. Recall that density = M/V where M is the mass of the sphere and V is the volume of the sphere. Is there a trend shown in the data that was obtained? How could you test this trend? If possible change the radius of the object and select a mass in such a way that the density of the object can be found on your graph. Does it fit in with the trend? If not, what are some possible reasons?

Next month we will discuss terminal velocity.

Da Vinci's parachute flies
"Leonardo Da Vinci was proved right on Monday, over 500 years after he sketched the design for the first parachute. "
Read more . . .

Terminal Velocity
"One pressure suit. One parachute. 130,000 feet. Two skydivers are racing to push the envelope of the stratosphere - and survive smashing the sound barrier on their way back down to Earth."
Read more . . .

Parachute Firsts

World's First Parachute Jump
"There was a crowd of people gathered to witness the event, and many of them turned their heads away when they saw the explosion, fearing it was the end of our friend GARNERIN. But, voila, here comes our hero under his homemade parachute, 10 meters in diameter, with a reported 30 square meters of canopy fabric and 36 suspension lines."
Read more . . .

Woman parachutist
"As far as is known, Sylvia made as many as 150 jumps at air shows and in front of military observers. She demonstrated the Guardian Angel in America in 1919 and in Denmark in 1920. She jumped at Copenhagen in a wind of 60 mph"
Read more . . .

History of Parachutes

Educational Resources