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Impact force of falling object

Impact force of falling object

Introduction: (Initial Observation)

Falling objects carry a force that is much higher than their weight. Such high forces can cause death, injury and destruction. Impact resistance material may be used to reduce the impact force and prevent injury or damages.

Safety helmet or hard hat, steel toe boots, rubber floors and cushioning materials used in packaging are all examples of material that reduce the impact force of falling objects

The purpose of reducing the impact force is usually protection of people or products that may be hurt or damaged due to the high impact force.

In this project you will study the effect of different cushioning material in reducing the impact force.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about the mechanics of a falling objects. Read books, magazines or ask professionals who might know in order to learn about the cushioning material that may reduce the impact force. Keep track of where you got your information from.

Following are samples of information that you may find:

Why falling objects have a high impact force?

The concepts of falling objects can be demonstrated by considering the following hypothetical examples. For each example, assume that the falling object is a bowling ball that weighs ten pounds.

In the first example, assume that the bowling ball is simply placed on your foot and permitted to rest there. You will feel the Force applied to your foot as a result of the ball’s weight. In fact, the Force applied would be ten pounds, the weight of the bowling ball. If we now raise the ball until it is waist high, or say two feet from the top of your foot, and then we drop the ball onto your foot, you will notice a significant increase in the Force applied to your foot. When the ball was resting on your foot, it was not falling, and therefore, did not possess Kinetic Energy. However, with the Kinetic Energy of 20 foot pounds (10.0 pounds x 2.0 feet) attained by the falling ball, the Force applied to the foot becomes quite painful if not injurious. Moreover, it is intuitively clear that progressively increasing the fall height of the ball creates progressively greater impact forces, although it is clear that the weight of the ball remains the same at ten pounds. This hypothetical verifies the supposition that increased Kinetic Energy through increased fall height will create a greater applied Force at impact.

In the second example let us assume that you are lying on your back on the floor and that we drop the same bowling ball from a height of one foot onto the front of your thigh. Of course, there would be a painful sensation as a result of the applied impact Force. However, it is doubtful that any major injury would occur from this experiment. But, if we drop the same ball from a height of one foot onto your forehead if your head is resting against the ground, the results would most probably be considerably more injurious. Aside from the fact that a person’s head is considerably more valuable in the scheme of things than a person’s thigh, the Force applied as a result of the head impact would be much greater than the Force of the same-ball-same-height impact against the thigh. Now, if we drop the same ball from a height of one foot above a foam pillow resting on your forehead, the Kinetic Energy at impact would be the same ten foot-pounds (10.0 pounds x 1.0 foot) as that of the experiment without the pillow, but clearly, the results would be different with resulting injuries either eliminated or significantly mitigated. This is because the Kinetic Energy was expended over a greater Work distance than when the ball strikes the head directly. Simply stated, the Force applied to the head is reduced by the pillow because much of the Work done involves compressing the pillow.


How do you calculate the impact force?

When an object falls, it attains Kinetic Energy, and a falling object’s Kinetic Energy can be calculated by using the following relationship if the weight of the object is known, and if the fall height is known:

Kinetic Energy = Weight x Fall Height

Thus, if a ten-pound object falls through a distance of ten feet before it strikes the floor, its Kinetic Energy at the point of impact would be 100 foot-pounds.

When a flexible surface is struck by a falling object, the Kinetic Energy of the falling object performs Work on the soft body. This Work is manifested by the deformation or compression of the of the surface. Furthermore, if the falling object is pliable, there will be deformation of the object, as well.

In physics, Work is defined as the Force required to move an object through a distance, or:

Work = Force x Distance

Also, from physics, we know that Work is equal to the amount of Kinetic Energy expended to perform the work, or:

Work = Kinetic Energy

And, the foregoing gives rise to the relationship:

Force x Distance = Weight x Fall Height

Finally, we can rearrange this relationship into a form that will yield the Force applied as the result of being struck by a falling object:

Force =  Weight x Fall Height


1. Weight is the weight in pounds of the falling object.

2. Fall Height is the distance in feet through which the object falls prior to impact.

3. Distance is the composite compression/deformation distance in feet of the struck object and the striking object during the impact.

What we have shown thus far is:

1. The greater the Kinetic Energy attained by a falling object, the greater the Force applied as a result of being struck by the falling object. Moreover:

a. Kinetic Energy is increased by increasing the fall height.

b. Kinetic Energy is increased by increasing the weight of the falling object.

2. Force applied can also be increased by reducing the distance through which the Work is performed.

Newton’s Second Law

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

Object Falling from Rest

As an object falls from rest, its gravitational potential energy is converted to kinetic energy. Conservation of energy as a tool permits the calculation of the velocity just before it hits the surface.

Since you know velocity, mass, and kinetic energy, can you predict the force of impact?

Impact Force from Falling Object

Even though the application of conservation of energy to a falling object allows us to predict its impact velocity and kinetic energy, we cannot predict its impact force without knowing how far it travels after impact.

If an object of mass m=kg is dropped from height
h = m, then the velocity just before impact is
v = m/s. The kinetic energy just before impact is equal to
K.E. = J.

But this alone does not permit us to calculate the force of impact!

If in addition, we know that the distance traveled after impact is
d =m, then the impact force may be calculated using the work-energy principle to be

Average impact force = F = N.

Note that the above calculation of impact force is accurate only if the height h includes the stopping distance, since the process of penetration is further decreasing its gravitational potential energy.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is comparing different cushioning material for their ability to reduce the impact force of a falling object. Possible material that we may test are: Shredded paper, Styrofoam peanuts, cotton, feather, water, balloon, sponge, rubber foam.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the type of cushioning material.

Dependent variable (also known as responding variable) is the impact force of a falling object.

Constants are the falling object, the falling distance and the thickness of cushioning material.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

This is a sample hypothesis:

My hypothesis states that among shredded paper, sponge, wood dust and cotton, sponge will be a better cushioning material and reduce the impact force the most.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Measure the impact force

Introduction: The impact force of a falling object is a function of the weight and height of the falling object as well as the distance traveled after impact. In this experiment we will test different cushioning material with the same falling object and use the same falling height. In this way the weight and the falling height are constants. In order to calculate the impact force, we only need to measure the distance traveled after impact. This is a challenge because most cushioning material act like a spring and push back up the fallen object as soon as it comes to a full stop. To know the distance traveled after the impact, we will insert a needle into the cushioning material, so the new position of the needle will show the distance traveled after impact (assuming that the needle does not move back up when the cushioning material decompress.


1. Prepare a wooden box with legs and a small hole in the middle. Feel free on selecting the box material and the exact dimension of the box; however, I suggest a box that is about 12 x 12 inches and the sides are about 4 to 5 inches high. The diameter of the center hole may be about 2 inches. Red line shows the position of the needle that you will insert later.

2. Fill up the box with one of the packing material that you want to test. Distribute the material evenly. If you are using foams, you may need to use multiple layers of the foam.

3. Insert a long needle in the center of the packing material. The end of the needle must be at the same level as the packing material. The other end of the needle must exit the hole. Mark the length of the needle that is out at the bottom of the box.

4. Hang a weight (a glass jar, a wood block or any similar object) right above the needle at a certain height. Feel free to setup your experiment for any height you like. Whatever height you select must be used for all your experimental trials. I suggest a height of about 2 feet or 50 centimeters.

5. Release the jar and let it drop on the needle at the center of the box.

6. Measure and record the length of the needle that exited the box as a result of force entered by the falling bottle. This will be the distance object traveled after impact.

7. Record your results in a table like this:

Cushioning material Weight of the falling object Falling height Distance traveled after impact Average Impact force
Cotton balls 1 kg 50 cm
Shredded paper 1 kg 50 cm
Sponge 1 kg 50 cm
….. 1 kg 50 cm

Calculate the average impact force for each cushioning material using the formula

Force = Weight x Fall Height

and write them in the last column of your results table.

Draw a graph:

Make a bar graph to visually present your results. Use one vertical bar for each of the material that you test. Write the names of the material under the bars. The height of each bar represents the average impact force.

Other experiment options:

Using a needle or wooden skewer is just an idea on how you may measure the compression distance of cushioning material. More advanced laboratories use weights attached to an arm that only move in one direction. In other words when the weight comes to a full stop, it will not be pushed back up.

Another method is using a video camera and a ruler. Slow motion playback of the recorded tape can show exactly how much the falling object traveled after initial impact with the surface of the material.

Experiment 2: Compare the impact force

Introduction: The impact force can be used to propel a projectile such as a steel ball upward in the open space or on a ramp. The distance or the height the projectile travels depends on the impact force.

In this experiment we use a falling steel ball to create the impact force and then use the travel height of the projectile (another steel ball) to determine the relative impact force.

In order to control the experiment environment and being able to make measurements, we use a ramp for the falling ball and the projectile ball.

This experiment is designed for students who want to compare different amounts of same type cushioning materials and see how do they affect the impact force.


Get two identical metal balls for your experiment. With the help of an adult, make a wide V-shape guide rail or ramp for your experiment.

The rail may be made of wood or aluminum. If you use wood, you may also use additional wooden legs or columns to hold it in position. For best results make the rail the same width as the balls, but make sure that the balls can travel along the rail easily and smoothly. The overall size of the balls and rails are optional. I recommend the steel balls that are about 18 mm (3/4th inch) in diameter and the overall length of the rail may be about 100 cm (40 inches).


  1. Place one ball (B) on the horizontal area of the rail and release the other ball (A) from the top of the right ramp of the rail. The moving ball (A) must hit the the stationery ball (B) and stop at the horizontal area and then ball B must move up the left ramp. See how far the ball B travels up the left ramp. Mark that place and measure the travel height. Repeat this a few times to make sure your measurements are accurate.
  2. Place small amount of packing materials in the horizontal area of the rail before the stationary ball and repeat your test. The packing materials must reduce the impact force of the moving ball (A) so that the second ball (B) will travel less up the left ramp of the rail. Record the travel height.
  3. Increase the packing materials or change the packing materials and repeat the above test. Make sure that ball A is always released from the top of the right ramp.
  4. Enter the travel height up the left ramp in your results table as a representation of relative or potential impact force.
Thickness of Cushioning materials Relative impact force

Make a graph

Use the above results table to make a line graph. Make 6 vertical lines to represent the relative impact force. Name the lines as the thickness of cushioning materials (5mm, 10mm, …) and write these names bellow the lines. The height of each line must represent the relative impact force. That is the same as the travel height up on the left ramp. Connect the top of all lines to make a line graph.


Why can you use the travel height of the ball on the left ramp to represent the relative impact force?

When the impact force is used to eject a projectile upward, it is first converted to kinetic energy so that the projectile will get moving. It is then changed to potential energy in the projectile (on the top of the ramp when the ball stops and is ready to role back down). That is why the elevation or upward movement of of the projectile has a direct relation to the impact force.

Impact Force = Weight x projection Height

Why can’t you measure the actual impact force?

The actual impact force also depends on the flexibility of the struck object. The impact force will be higher on hard – stationary objects; it is less on flexible or easily movable objects.

Materials and Equipment:

Material that you test may vary. Make sure to list all the material that you test in this part of your report. In addition you must also write the name of equipment that you use. This is a sample:


  1. Cotton
  2. Shredded paper
  3. Sponge
  4. Styrofoam


  1. Wooden Box
  2. Needle or wooden skewer
  3. Cone shape weight
  4. Ruler
  5. Video Camera (optional)

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


Write your calculations in this section of your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


Visit your local library and find books related to force, motion, plastics and packaging. Review the books and look for additional information that may be useful for your project. List such books as your references in the reference section or bibliography of your project report.

Question: We’re working on the Impact force of a falling object and comparing various materials ability to absorb the energy of the impact. Our idea is to build a Tupperware container to hold an egg which has been shaken a questionable amount of time to blend the yolk and whites. Position the egg in the container for consistency of impact. To test recycled material, maybe shredded paper, Styrofoam pellets and shredded plastic bottles. Comparing the best of the three examples to water and a pressurized large balloon. We’ll be using F=MA for the dropped item. We’re not sure how to calculate the energy transfer of the various materials besides height measurements. Any suggestions to improve the experiment and more accurate measuring.

Answer: I did not understand about the egg and shaking it. I think you want to drop an egg. Why don’t you drop a marble or a stone?
Either way, first you need to calculate the kinetic energy of the falling object at the contact point.
Kinetic energy of a falling object KE=mgh
To calculate the impact force, you will also need to know how much did the object travel after impact until it comes to a full stop.
Average impact force x distance traveled = change in kinetic energy
As you can see here, as the travel distance increases, the impact force reduces.
Since this subject is not listed in our website, I will add a project page for that and let you know later.

Question: I did the experiment, and I don’t understand the results. The less the wooden stick traveled after the impact the bigger the impact force. and I thought it had to be the other way around. The less that the wooden stick actually moves the more it reduces the impact force.. so can you guys explain this, please.

Answer: Hold your hand up, in front of yourself and ask a friend to drop a heavy object into your hand. The heavy object will push your hand down, so it will not be very painful because the impact force is low. Now, ask your friend to do it again, but this time, place your hand on a table so that it cannot move down by the falling object. This time you will fill pain caused by a higher impact force.

When the impacted object travels more, the impact force is less. Impact force will be the highest if the object does not travel at all.

So the packing material that made the needle or stick travel more, will minimize the impact force and is a better choice.

Good packing materials are very elastic (like spring) in the range of forces they may be impacted. So the packing materials used for heavy and high density objects are not the same as packing materials for light and low density objects.

Question: I was wondering why you have to stick a needle in the middle and how that will help measure the impact force for when it comes back up?

Answer: When a moving solid object hits a cushioning or elastic object, it will bend or deform that object for a very short period of time. In order to measure the impact force we need a method to measure or record the depth of bending or deformation. A needle that can be pushed inward, but it does not eject back can be a good method to record and measure the amount of deformation.