# Free falling

### Scenario information

Subject: Physics

Correlations and Interdisciplinarity:

• Mathematics
• Informatics
• History
• Biology
• Use of information and communication technologies

Find tips and instructions for using digital teaching tools at e-Laboratory. (in Croatian Language)

Key Words: weightlessness, 2nd Newton’s law, gravitational force, drag, free fall, free fall acceleration, buoyancy.

Learning outcomes:

• describe and graphically display uniform accelerated motion (A., B.)
• with the help of computer simulation analyze the impact of drag and buoyancy on free fall of the body (B.)
• apply 2nd Newton’s law to solve problems and motion analysis (B., C.), describe free fall (A.C.)
• explain weightlessness (C.)
• investigate motion using motion detectors, motion records and/or computer simulation (A., B., C.)

*In parentheses are letters indicating the teaching scenario activities, and their implementation contributes to achieving the respective outcomes.

### Activity description

#### A On the way down

It is well known that animated films are subject to different laws than in real life, and one of them states that gravity begins to act when the hero realizes that he is above an abyss. This law is beautifully noticeable in the video, with a duration of 0:57 min. It is a popular black-humor animated film about a coyote and a bird runner. However, after the coyote realizes that he should fall, gravity takes over.

How do bodies move when only gravity acts on them?

Discuss with your students about the motion of the body under the influence of gravity in the case where we can ignore other forces. Let students make assumptions about the movement of the ball when it is allowed to free fall (drag is ignored).

You can analyze free fall in several ways. If you have the time and opportunity, it would be good to conduct all three tests and compare the results obtained.

Experiment 1 Free-fall analysis with video analysis software

Divide students into groups.

Let students record the free fall of a ball in front of a contrasting canvas and analyze the recording with the aid of the movement video analysis program Tracker.

Three balls of different masses, a contrasting background, an object of known length (this can be both a measuring tape or a metal scale stick) are required for performing the experiment.

Instruct the students to place the recording device at a far-enough distance while recording, making sure that they capture vertically on the plane with a contrasting background. The object of a known length, such as a stick, should be set so that it can be seen in its entirety in the frame. Let the students begin recording and release the ball from a height of 1.5 m to freely drop in front of the contrasting background. Repeat the experiment with all three balls.

After shooting, analyze the motion in Tracker. Simultaneously present the footage and graphical presentation of the ball motion to students on a projector. Discuss how a body’s motion affects the look of a particular graph and connect the motion with its mathematical and graphical description. Let the students conclude what kind of motion it is and calculate the acceleration of free fall g.

Experiment 2 Free fall analysis using an electromagnetic ticker

Conduct the analysis of the ball drop by demonstrating it with students using an electromagnetic ticker. Attach the tape to the top of the ball and allow it to fall freely from a height of 1.5 m (the tape passes under the hammer of the electromagnetic ticker). Watch the tape. Let students look at the record and conclude what type of motion it is (due to acceleration the distances between dots on the record will be increasingly greater). By counting dots, have them determine the falling time and create a table in the dynamic math program Geogebra in which they will enter the path taken and time and the result for acceleration of free fall with the help of a mathematical formula for accelerating free fall.

Experiment 3 Free fall analysis using an interactive measuring instrument

Have the students measure the acceleration of free fall with the help of an interactive measuring instrument. Re-use balls as previously.

Note: Set the distance sensor at a distance of 1.5 m from the floor with a sampling frequency of 25/s. To analyze data, use the functions Marker and Crop for cutting out parts that do not show free fall on the record (the moment of the ball’s bouncing off the surface). Using quadratic regression, an equation is obtained, and the acceleration of free fall is calculated.

Students should compare the figure for free fall acceleration obtained in all three methods and calculate the experiment error by comparing the empirical result with the theoretical value of g. Ask them: How would you explain the differences between the theoretical and empirical value g?

The first man who experimentally tested the motion of the body in free fall was Galileo Galilei. Talk to the students about his role in the development of modern science and the problems he had due to his own, at the time, revolutionary research.

If some of the students want to, have them create a poster about Galileo’s influence on science, introduction of the scientific method, and the importance of physics trials with the help of a tool for creation of infographics, reports, posters, and presentations, Piktochart, which can be printed and placed in the Physics classroom.

Support procedures

A student with disabilities who will participate in the activity of analyzing the footage with the help of the Tracker tool should be supported in this by gradually guiding them into the demonstration of the tool’s operation and then (if possible) let them run the task independently. In the oral analysis of videos, some students with disabilities (e.g. with specific learning difficulties) will find that questions that need to be answered facilitate presentation, while the task in which they need to talk about what they observed will be the more difficult part of the presentation, where they may not be able to do so well. With the aforementioned students (with specific learning difficulties) and students with attention and hyperactivity disorders, check their understanding of those physical quantities that are needed for computing in the activity. Likewise, when comparing the rate of acceleration of free fall, allow them to use reminders with mathematical formulas and the use of a calculator.

#### B Jumps from the “edge of space”

Talk to your students about what parachute is for and the forces that act on the parachute.

What would falling without a parachute from a height of several thousand meters look like? Discuss what forces would then work on the jumper.

Show the students a video, with a duration of 2:01 minutes, where we can see Luke Aikin jumping out of an airplane without a parachute or a special jumper suit at a height of 7,600 m. He falls onto a special net that is set up at a height of approximately 60 meters from the ground, at a speed of approximately 190 km/h.

Discuss with the students why it is necessary to set the net at a certain height, as well as the speed of impact. Ask them to calculate at what speed he should hit the net if the height information is included in the known formula for speed at free fall, then compare that value with the speed that has been reached. Discuss what affects that speed.

Point students to the simulation. Switch the simulation to manual settings. There they can observe the fall of the body by altering the body’s properties: mass, radius, initial velocity, and density of the medium and wind speed. The simulation can be slowed down with the help of the option simulation rate. Turn on the option show forces on object to get a vector view and the figure amount of gravity, drag, and buoyancy that act on the body and the resultant (total) forces. Tell students to choose a height from which the body falls, and an initial speed of 0 m/s. Change the mass of the body with a constant radius, then the radius with a constant mass. They will observe the time of the fall and the forces that work: gravity, buoyancy, drag, and resultant force.

Discuss with the students how the time the body needs to fall depends on the body mass and radius.
Ask the students to describe the motion, in which section it is accelerated, and in which it is uniform.
Let them explain how motion is affected by forces acting on the body and compare their observations by looking at the graph, by turning on the option graph, and option table can display the current speed and acceleration values in every hundredth of a second of the path.

Discuss what parameters buoyancy depends on, and which parameters drag depends on.

Note: The drag increases with the square of the speed and becomes constant at the point when the motion has become uniform.

But drag also depends on the “impact surface”, but this is not seen in the simulation, so talk about it in principle, citing examples from life, e.g. what we mean when in everyday life we say that some vehicle
is “aerodynamic”. Discuss, for example, the shape of a racing car, sail, and parachute.

Have students create an animation in groups with the help of the animation tool Animatron which will show the jumper jumping without a parachute with marked forces that act on him.

For students who were interested in the topic of the introductory video, point out the video (Eng. Felix Baumgartner’s Space Jump World Record 2012), with a duration of 19:54 min. This is the official footage of Felix Baumgartner’s jump, who jumped from 39,045 m in 2012 and broke the sound barrier during free fall, reaching a maximum speed of 1,342 km/h.

Talk to students about “extreme sports” and the examples they provide. How does doing such sports positively affect our health and personality?

Support procedures

Although the simulation is simple to use, one example in a simulation can be performed with students with disabilities for them to understand all parameters and diagrams. When solving tasks, if necessary, let students (e.g. with specific learning disabilities, attention deficit and hyperactivity disorders) use reminders with explanations of physical size markings and mathematical formulas required for computation.

In Didactic-methodological instructions for natural sciences and mathematics for disabled students (in Croatian Language) you can find additional instructions on how to engage students in the activity of watching videos and network simulations.

Even though the simulation in this activity describes the topic in a very vivid way, some disadvantaged students will also require a separate overview (in the form of a written summary) of the most important conclusions that have been made using the aforementioned simulation.

During the discussion on the types of extreme sports (especially if you have students with behavioral problems or students with attention and hyperactivity disorder), it is important to remind students (and warn them) that any type of sport, including extreme sports, requires education, training, and respect for certain rules in order to preserve the health and safety of all athletes.

#### C When you fall, but you float!

Talk to students about weightlessness. When do we say that a body is weightless? Is it possible under the conditions of Earth’s gravity?

Show them the video Liquid Ping Pong in Space with a duration of 1:05 min., taken at the International Space Station (ISS), which is in a permanent orbit around the Earth.

Discuss with students whether the astronaut and the water in the video are affected by Earth’s gravity.

If there was no influence of Earth’s gravity, how would the station remain in orbit around the Earth?

To solve the problem, perform a simple experiment.

Experiment 4 Inertial force in a free fall system

Hang a weight on a dynamometer and weigh it. Have a student take the dynamometer in their hand and stand on a table and jump off the table holding the dynamometer in their hand. If needed, repeat the experiment several times, but make sure that no injury occurs.

What happens to the weight of the weight when it falls?

Consider the impact of inertial force acting on the weight because the system in which it is located is accelerating. Have the students describe the experiment and draw conclusions and, using the tool Web Whiteboard, have them sketch a force diagram acting on a falling weight.

Note: Instead of jumping from the table, the student can hold the dynamometer in his hand while riding the elevator and record the changes that are taking place.

Now discuss weightlessness in a space station in Earth’s orbit.

Discuss other possible situations, such as a falling elevator, an airplane diving in a loop, etc.

Have them display one of the situations you discussed with a plaque in the tool Canva.

Point interested students to the link where they can play virtual basketball in a state of weightlessness. In a short video that can be skipped, an astronaut demonstrates throwing a ball through a hoop in weightless conditions.

Support procedures

Immediately before performing the experiment involving jumping with a dynamometer, remind the student (e.g. student with attention deficit and hyperactivity disorder) of the instructions on how to perform the experiment and what to look for. Some motor activities may further excite the aforementioned students, who may later require additional time to focus on other activities.

When describing a performed experiment to students with disabilities (e.g., students with specific learning disabilities, students with attention deficit and hyperactivity disorders) provide them with guidelines or structure that the description of the experiment should contain. You can also ask the students a few questions regarding the experiment that the students will respond to, which will guide them to what they need to write.

In Didactic-methodological instructions for natural sciences and mathematics for disabled students (in Croatian Language) you can find additional instructions on how to engage students in the activity of watching videos and the use of digital tools.

#### For students who want to know more

On social networks we often come across claims that humanity was never on the Moon and that the photographs and footage from the Moon were faked.

Have students who want to know more analyze the recording Feather & Hammer Drop on the Moon, with a duration of 0:47 minutes at home with the help of the video analysis software Tracker and determine the acceleration of free fall g on the Moon.

Point the students to the website, where they can also download the footage and find the necessary data for analysis and find out more about the Apollo 15 mission.

Have students take a screenshot and present their results to the rest of the class or share it on the social network Yammer.

Talk to your students about whether it was possible to use special effects from nearly 50 years ago to make persuasive faked footage about being on the Moon like this.

Take the opportunity to talk to students on how conspiracy theories can be disproved through the use of science.

One of the questions posed by conspiracy theorists is: If gravity is weaker on the Moon, how does dust fall so quickly to the surface?

Show the students the video Dust, in the duration of 0:12 min. Have the students watch the movement of dust. Discuss why it moves in such a manner.

Note: Dust rises and falls in a parabolic path without swirling, which would not be possible in Earth’s atmosphere, and this is evidenced by many films that have been filmed on landing on the Moon. In fact, the reason dust falls so slowly on Earth is exactly drag.

You can find additional clarification of terms on relevant web pages