The Physics of GriGri | When does No-Hands Belay Fail?

Summary

This video explores the intricacies of how the GriGri belay device works and when it might fail. Through a series of experiments, the creator demonstrates how the GriGri can slip in a 'no-hands' situation, especially when there's minimal tension on the brake side of the rope. The video dives into the physics of rope tension, friction, and cam engagement, showcasing real-world tests with various ropes and weights. Despite these findings, the GriGri remains one of the safest belay devices, and the video concludes with a recommendation for further learning through Brilliant.org.

Takeaways

• ⚠️ GriGri devices can slip even in a no-hands situation, and it's crucial to understand when and how it happens.
• 👀 If the GriGri's cam is pressed, it won't lock, even if the climber falls, which is a safety concern.
• 🧤 Bringing a big loop of slack while pressing the GriGri's cam can lead to burns or slippage through the belayer’s hands.
• 🔧 The GriGri’s cam engages based on the tension on the brake side of the rope, not the climber’s side.
• 📐 Rope tension depends on factors like weight, angle, and friction between the rope and GriGri's cam.
• 🧪 Experiments show that if there's no tension on the brake side, the GriGri cam will not engage, increasing the risk of slipping.
• ⚖️ Different ropes (stiff or soft) influence the GriGri’s performance, with softer ropes more prone to slippage.
• 💡 The angle and direction of the rope entering and leaving the GriGri can significantly impact its locking mechanism.
• 💪 Heavier weights on the climber’s side do not affect the GriGri’s engagement—it relies only on the brake side tension.
• 🎓 Older, worn-out GriGri devices may have looser springs and could engage more reliably than newer models.

Q & A

What is the primary issue being discussed in the video?

The video discusses how the Grigri, a belay device, can slip in certain no-hands situations, even though it's designed to lock automatically when tension is applied to the rope.

How can pressing on the Grigri's cam cause a failure in locking?

If someone presses on the Grigri's cam while a climber falls, the cam won’t engage, preventing the device from locking properly, which can be dangerous.

What happens if the brake side of the rope has no tension?

If there is little to no tension on the brake side of the rope, the Grigri may not engage and lock, even if significant force is applied to the climber’s end of the rope.

How does the angle of the rope entering and leaving the Grigri affect its performance?

The angle at which the rope enters and leaves the Grigri is important. If the rope follows a smooth arc, there is less friction, which can prevent the Grigri from locking properly. Conversely, more abrupt angles create higher friction, making the device more likely to lock.

Why is the brake side of the rope critical for the Grigri to engage?

The brake side of the rope controls the tension that determines whether the cam in the Grigri will engage. Without sufficient tension on the brake side, the cam does not lock, regardless of the load on the climber’s end.

Does the weight of the climber affect the Grigri’s ability to lock?

No, the Grigri’s ability to lock primarily depends on the tension on the brake side of the rope, not the weight of the climber.

What role does rope type and diameter play in the Grigri's performance?

Softer and skinnier ropes are more likely to slip through the Grigri, while stiffer ropes are less prone to slippage. Even ropes of the same diameter but different stiffness can behave differently.

What surprising result did the user find when comparing a new Grigri with an old, worn Grigri?

Contrary to expectations, the worn Grigri with a looser spring engaged more reliably than the new Grigri because the looser spring caused the cam to engage more easily.

What external conditions make it difficult for the Grigri to slip during use?

The Grigri only slips under very specific conditions, such as having minimal tension on the brake side, smooth rope paths, and low friction. Even when trying to induce slippage, the user found it challenging to make the Grigri fail consistently.

How does friction play a role in the overall belaying system using a Grigri?

Friction between the rope and other parts of the belay system, such as quickdraws or pulleys, reduces the effective load on the Grigri, affecting how much force is transferred through the rope. This friction helps support the climber and may reduce the strain on the Grigri.