It is well known that cartoons are subject to somewhat different laws than real life, and one of these states that gravity exerts itself when the hero or heroine realizes that they are above an abyss. This law can be clearly observed in this popular black-humour video featuring Wile E. Coyote and the Road Runner (0:57 min). However, when Wile E. Coyote realizes he is supposed to be falling, gravity takes over.

How do objects move when only gravity acts on them?

Discuss the motion of objects affected by gravity in cases where other forces can be ignored. Ask the students to share their ideas about the motion of a free-falling ball (drag is ignored).

You can analyse 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.

Test 1 Free fall analysis using video analysis software

Divide the students into groups.

Have the students record a free-falling ball in front of a canvas in a contrasting colour and analyse the recording with the aid of the video analysis tool Tracker.

To perform the experiment you will need three balls of different masses, a background in a contrasting colour, and an item whose length can be measured (a measuring tape or a scale stick).

Instruct the students to place the recording device far enough to capture the movement, making sure that they are filming the contrasting background vertically. The object whose length can be measured should be placed so that it can be seen in its entirety in the recording. Have the students drop the ball from a height of 1.5 m and record it in free fall in front of the contrasting background. Repeat the experiment with each of the three balls.

Now analyse the motion in Tracker. Use a projector to have the students view and compare the recorded footage and a graphical representation of the ball moving (for each of the three balls). Discuss how the motion of an object affects the look of a particular graph and point out the link between the motion and its mathematical and graphical description. Let the students conclude what kind of motion it is and calculate the acceleration of free fall g.

 Test 2 Free fall analysis using a ticker timer

Demonstrate dropping the ball using a ticker timer. Attach the ticker tape to the ball and allow it to fall freely from a height of 1.5 m (the tape passes under the hammer of the ticker timer). Then have the students look at the tape and conclude what type of motion this is (due to acceleration, the distances between the dots on the tape will be increasingly greater). The students should count the dots and thereby determine how long it has taken for the balls to fall. Have them create a table in the interactive mathematics app Geogebra – they will need to enter the distance covered and the time required for this, as well as the result for free fall acceleration with the help of the relevant mathematical formula.

Experiment 3 Free fall analysis using an interactive measuring instrument

Have the students measure free fall acceleration with the help of an interactive measuring instrument. Use the three balls as before.

Note: Set the distance sensor at a distance of 1.5 m from the floor with a sampling frequency of 25/s. To analyse the data, use the functions Marker and Crop to crop parts that do not show free fall (the moment the ball bounces off the surface). Use quadratic regression to get the equation needed to calculate free fall acceleration.

The students should compare the figures for free fall acceleration obtained in all three experiments and calculate experimental error by comparing the empirical results with the theoretical value of g. Ask them: How would you explain the differences between the theoretical and empirical value of g?

The first person to experimentally test the motion of free-falling objects was Galileo Galilei. Talk to the students about his role in the development of modern science and the problems he experienced due to his research, which was revolutionary at the time.

Some of the students may want to create a poster about Galileo's impact on science, the introduction of the scientific method, and the importance of experiments in physics. They can use Piktochart, a tool for the creation of infographics, reports, posters, and presentations. Their posters can be printed out and hung in the Physics classroom.

Activities to support Special Education Needs students

Students with disabilities who will participate in analysing the footage with the Tracker tool should receive the following support: give them a step-by-step demonstration of how the tool works and then (if possible) have them do the task independently. When they discuss the videos, some students with disabilities (e.g. those with specific learning difficulties) will find it helpful to have specific questions which they need to answer, because making independent observations may be too challenging. If you are teaching students with specific learning difficulties or students with attention and hyperactivity disorders, check if they understand the symbols for those physical quantities that are needed to perform the planned calculations. Likewise, when they compare the different values for free fall acceleration, allow them to check mathematical formulas and a calculator.

Talk to your students about what parachute is for and which forces are acting on someone who is making a parachute jump.

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

Show the students a video (2:01 min.) of Luke Aikins jumping out of an airplane without a parachute or a “wingsuit” from a height of 7,600 m. He drops at a speed of approximately 190 km/h and lands on a special net that is set up at a height of approximately 60 meters from the ground.

Discuss the speed of impact with the students and have them suggest why it is necessary to place the net at a certain height. Ask them to calculate what speed Aikins is travelling at when he lands on the net, if the height he jumped from is included in the formula for calculating speed in free fall. Students should compare the result with Aikins’ actual speed. Discuss possible effects on that speed.

Point students to the simulation and switch the settings to manual. The students can observe how the fall of an object is impacted if its properties (mass, radius, initial velocity, density of the medium, and wind speed) are altered. The simulation can be slowed down by adjusting the simulation rate. Choose show forces on object to get a vector view and see the values for gravity, drag, and buoyancy that act on the object, as well as the total forces. Tell students to choose a height from which an object falls and the initial speed of 0 m/s. They should alter the mass of the object, keeping the radius constant, then vice versa. The students will observe the duration of the fall and the forces at work: gravity, buoyancy, drag, and resultant force.

Discuss with the students how long it takes for an object to fall, depending on mass and radius. Ask the students to describe the motion and say when it is accelerated and when it is uniform.

Have them explain how motion is affected by the various forces acting on the object and compare their observations with what they see on the graph. They need to use the graph option to do this, while they can use the table option to display the current speed and acceleration values for every hundredth of a second of the path the object travels. Discuss which parameters buoyancy and drag depend on.

Note: Drag increases with the square of speed and reaches a constant when motion becomes uniform. However, drag also depends on the impact surface but as this can’t be observed in the simulation, discuss it in general terms, citing examples from everyday life. You can, for instance, explain what we mean when we ​​say that a vehicle is "aerodynamic". Discuss, for example, the shape of a racing car, a sail, and a parachute.

Have students work in groups use the Animatron tool to create an animation which will show a person jumping without a parachute, with the forces acting on him or her clearly marked.

Students who were interested in the topic of the introductory film may want to watch the Felix Baumgartner's Space Jump World Record 2012 video (19:54 mins.). This is the official footage from 2012 showing Felix Baumgartner jump from a height of 39,045 m and reach the maximum speed of 1,342 km/h, breaking the sound barrier in free fall.

Talk to the students about extreme sports and the examples they provide. How do these sports positively affect our health and personality?

Activities to support Special Education Needs students

Although the simulation is simple to use, you can have students with disabilities do an example with you, so they will understand all the parameters and diagrams more easily. As they do the various tasks, if necessary, let the students (e.g. those with specific learning disabilities, attention deficit and hyperactivity disorders) check physical quantities and the mathematical formulas they need to complete the tasks.

In the handbook Didactic-Methodological Instructions For Natural Sciences And Mathematics For Students with Disabilities (in Croatian) you can find additional instructions on how to engage students in the activity of watching videos and online simulations.

Even though the simulation in this activity presents the topic in a very vivid way, some students with disabilities will also require a separate overview (in the form of a written summary) of the most important conclusions reached as a result of using the simulation.

During the discussion on extreme sports (especially if you have students with behavioural 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 training and compliance with rules in order to preserve the health and safety of all athletes.

Talk to students about weightlessness. When do we say that an object is weightless? Is this possible, given the laws of gravity on Earth?

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

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

If it weren’t for the Earth’s gravitational pull, how would the station remain in orbit?

Perform a simple experiment to answer the question.

Experiment 4 Inertial force in a system in free fall

Attach a weight to a dynamometer and measure how heavy the weight is. Have a student take the dynamometer, stand on a table, and jump off it, holding the dynamometer in their hand. If necessary, repeat the experiment several times, but make sure that no injury occurs.

What happens to the weight of the weight as it is falling?

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 Web Whiteboard tool, have them sketch a diagram of the forces acting on a falling weight.

Note: Instead of jumping off the table, the student can hold the dynamometer in his or her hand while riding the elevator and record the changes 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.

The students can prepare a poster using Canva to present one of the situations you’ve discussed.

Point interested students to the link where they can play virtual basketball in weightless conditions. There is an optional short video in which an astronaut demonstrates throwing a ball through a hoop in weightless conditions.

Activities to support Special Education Needs students

Just before they do the experiment which involves jumping off the table with a dynamometer, remind the students (e.g. those with attention deficit and hyperactivity disorder) once again what they need to do and what to observe. Some motor activities may further excite these students, who may later require additional time to focus on other activities.

When they are required to describe the experiment they have done, students with disabilities (e.g., those with specific learning disabilities, students with attention deficit and hyperactivity disorders) should be provided with guidelines or the structure which their description should follow. You can also ask the students to answer a few questions about the experiment to guide them in their writing.

In the handbook Didactic-Methodological Instructions For Natural Sciences And Mathematics For Students With Disabilities (in Croatian) 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 man was never on the Moon and that the photographs and footage from the Moon were faked.

Have students who want to know more analyse the Feather & Hammer Drop on the Moon video (0:47 mins.) outside class with the help of the video analysis software Tracker. Ask them to determine the acceleration of free fall g on the Moon.

Point the students to this website, where they can download the video and find the data they will need for their analysis, as well as find further details about the Apollo 15 mission.

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

Talk to your students about whether the special effects of approximately 50 years ago were adequate to create convincing fake footage of being on the Moon.

Take the opportunity to talk to the students about how science can help to disprove conspiracy theories.

This is one of the questions posed by conspiracy theorists: If gravity is weaker on the Moon, why does dust settle so quickly on the Moon’s surface?

Show the students the Dust video (0:12 min.). Have the students observe how the dust in the video moves and discuss why this is so.

Note: Dust rises and falls following a parabolic path without swirling, which would not be possible in the Earth's atmosphere, as evidenced by many films dealing with the topic of lunar landing. In fact, the reason dust settles so slowly on Earth is precisely drag.