Time and Space | Posts Filtered by Tag

Ever since 1996, when Ingmar Backman did his legendary backside air up in Riksgränsen, I’ve been wondering: how big can a human actually go in a quarter — purely in theory?

Today, approximately 29 years later, I finally chat:ed my way to the answer (feel free to double-check the math and send feedback).

With the right height and transition on the quarterpipe, and a carefully calculated speed that a pair of well-trained thighs can withstand. I’ve come up with this:

I crunched the numbers using the laws of physics and assumed the rider can handle 4 g in the transition. Here are the formulas and calculations:

1. Total g-force in a quarterpipe:

g_total = (v² / (r × g)) + 1

Where:

• `v` = speed in m/s

• `r` = radius of the quarterpipe (in meters)

• `g` = 9.82 m/s² (gravitational acceleration)

2. Maximum speed without exceeding 4 g:

v² = (4 − 1) × r × g = 3 × r × g

3. Converting speed to height (all kinetic energy → height):

h = v² / (2g)

Insert v² from above:

h = (3 × r × g) / (2g) = (3/2) × r = 1.5 × r

So the maximum height above the lip becomes:

h = 1.5 × r

4. Example with a 20-meter radius quarterpipe:

h = 1.5 × 20 = 30 meters (above the lip)

Total height from ground = 20 + 30 = 50 meters

5. Speed required:

v² = 3 × 20 × 9.82 = 589.2

v = √589.2 ≈ 24.26 m/s ≈ 87.4 km/h

```

Conclusion:

If you have a quarterpipe with a 20-meter radius and can handle 4 g in the transition — then, theoretically, you can pull off a 30-meter-high air.

So... what are you all waiting for out there?

Ingmar Backman at the apex of his remarkable jump

Ingmar Backman's backside air, Riksgränsen Sweden, May 1996

My Reaction

My first response built on the assumptions in the OP. Given a landing in a 20-m radius quarter pipe, the maximum g's occur at the bottom of the quarter pipe, where normal force is opposite weight, not at the lip, where normal force is perpendicular to weight. So the calculation shows maximum height from the bottom of 30 m, and maximum height above the lip of 10 m, ignoring friction and air resistance.

If the person center frame is 1.8 m (71") tall, the height of this jump is 1.8•4.6 = 8.3 m above the lip, a good fit for a theoretical maximum of 10 m.

Then I Googled for and watched video of the jump. I realized some of the assumptions in the OP needed revision. The launch speed was limited by the terrain of the lead-in to the quarter pipe, and the ability of the rider to max out on speed during the lead-in. The landing zone could definitely not be modeled as a circular arc. Better to model it as a steep inclined plane, with landing impact on the slope. And finally, the parabolic trajectory of the jump is too large to ignore. The take-off ramp was not vertical at the lip.

To achieve a jump height of 8.3 m, the vertical component of Ingmar's speed at the lip would have to be 13 m/s, or 29 mph. With the angle of the ramp taken into account, the resultant speed would be no more than 15 m/s, or 34 mph. The long, uphill lead-in to the ramp scrubbed off a lot of speed.

Here is a good analysis of g's during snowboard landings, and the impact of a sloped landing zone. While in theory snowboarders might experience 14 g's at landing, the actual number is usually quite a bit less. What matters is the impact velocity perpendicular to the slope, and the time it takes for that velocity to zero out.

Frame-by-frame analysis of the landing shows that Ingmar bends his knees some, but also bends hard over at the waist, allowing his lower body to continue falling, and almost allowing his head to graze the snow. The sequence takes 5 frames or 0.2 seconds.

If the speed at impact is 15 m/s, and the angle between the slope and that velocity is 40 degrees, the component of velocity perpendicular to the slope would be no more than 10 m/s. With a stopping time of at 0.2 seconds, the stopping force would be 5 g's, what a roller coaster rider might experience and close to the 4-g maximum assumed in the OP.

For comparison, a Google search yields some compelling analysis to suggest that g's during carved turns are usually less than 2 g's and more often around 1 g or less. For quick reference, a turn at 15 m/s with a radius of 20 m yields a little over 1 g. But these are sustained g's, and they likely wobble quite a bit around the time-averaged value due to bumps and corrections to form.

Estimating the height of the jump

A still frame showing Ingmar's landing posture

Conclusion

Ultimately, the limitation on height of a snowboard jump is speed and angle of approach going into the jump, and the ability of the human body to absorb the forces needed to land. All in all, what a fascinating opportunity to explore the physics of snowboarding.

Share this:

Link: https://shelterphysics.com/blog/Quarter-Pipe-Heights-a1/

April 20, 2025
Is Energy "Lost" When It Changes Forms?

A while back, I had a series of interactions on FB which reveal common gaps in folks' understanding of energy conversions and conservation of energy.

The meme above sparked the conversation.

To dispense with a pet peeve of mine at the start, heat is a process of energy transfer, distinct from another process called work. What the meme should say is that the other energy is converted to thermal energy, a form of energy produced during the process of heating something up.

Numerous commenters refused to believe that heaters could be 100% efficient because they had learned that some energy is "lost" when it is converted from one form to another. It was clear what they meant is that a certain amount of energy would disappear, a clear violation of the law of conservation of energy. These commenters remind us that students will cheerfully hold conflicting ideas in their minds until teachers force examination of the conflict, and that describing energy as "lost" is perhaps not the best choice of words.

Some commenters referred to sound or light emitted from the heater as "wasted" energy. I countered that sound is just organized thermal energy, which would disorganize soon enough and warm the room. And that light from the element of a heater, if it did not go out a window, would be absorbed by the air or by surfaces in the room, and converted to thermal energy. Now we had begun to get to the heart of the matter.

There is no law of physics that requires energy to be "lost" or "wasted" during energy transfers. Earth has been orbiting the Sun for over 4 billion years, with continuous transfers of kinetic energy to gravitational potential energy and back. The second law of thermodynamics refers specifically to entropy, the concept that not all of the thermal energy available to a heat engine can be converted to mechanical energy. As a practical matter, devices with moving parts (and that includes electrons moving in a wire) are subject to friction, which produces thermal energy from kinetic energy and reduces the efficiency of the device.

Most of us would agree that the purpose of a heater is to heat the air in a room. If that is our definition of the outcome, it's tough to argue that the heater is significantly less than 100% efficient. Even a vortex heater which emits no light and circulates air across its elements will itself be warmed, and that warmth will eventually dissipate to the room. To find sources of inefficiency, we would need to follow the source of the electrical current being used by the heater until the wires carrying it are not in the room. I suppose one could argue that thermal energy absorbed by objects in the room and not the air inside it constitutes loss. As is often the case in physics, the definition of what is inside the system vs. what is part of the environment outside the system determines the mathematical process and outcome.