In simple terms, Gravitational Torque happens when gravity pulls on a part of our body that isn’t directly supported, creating a “tipping” force around a joint. Here are everyday examples of how we constantly fight or use this force:
- Bending over to pick something up: when we lean forward, our upper body creates a massive amount of torque on our lower back (the pivot). This is why our back muscles have to work so hard to keep us from face-planting, and why it’s easier to lift things by bending our knees.
- Arm fatigue while holding a phone: if we hold our arm straight out in front of us, we experience our hand and forearm far away from our shoulder (the pivot). This creates a long “lever arm,” making the torque high and our shoulder tire out quickly. If we fold our elbow to our side, the torque decreases and the phone is much easier to hold.
- The “Head-Nod” when falling asleep: our head is like a heavy ball sitting on our neck. When we are awake, our neck muscles counteract the gravitational torque. When we doze off, those muscles relax, and gravity wins, causing our head to tip forward or to the side.
- Walking and Balance: every time we take a step, our center of gravity moves outside our base of support. Gravity creates torque that tries to tip us over. We prevent the fall by swinging our opposite arm (using the Crossed-Kinetic Chain) and quickly placing our foot down to create a new support point.
- Using a wrench or opening a heavy door: while not a body part, we experience this when we push a door at the edge furthest from the hinges. Gravity pulls the door down, but we use torque to rotate it. If we try to push a door near the hinges, it’s much harder because we have less “leverage” to overcome its resistance.
When skiing, gravitational torque is the force constantly trying to “tip” our body planes around our boots/skis. How we manage this determines whether we carve a perfect turn or suffer a face-plant. Here are some examples on the slopes:
- Leaning too far back (“Backseat Posture”): if our weight shifts to our heels, gravity pulls our center of mass behind our boots. This creates a backward torque that makes our skis shoot out in front of us, making it nearly impossible to steer.
- Initiating a Turn: to start a turn, we intentionally shift our weight forward and slightly to the side. Gravity then creates a torque that tips our body into the turn. We “fall” into the curve but use our edges to catch ourselves and redirect that energy.
- The “Face-Plant” on Bumps: when we hit a mogul without absorbing it, the skis slow down abruptly but our upper body keeps moving. Gravity pulls our torso forward, creating a massive forward torque around our ankles that can flip us over the ski tips.
- Counter-Balancing (The Banana Shape): to keep from falling inward during a sharp, high-speed turn, we tilt our upper body away from the slope while our hips stay closer to the snow. This adjustment moves our center of gravity to balance out the torque created by both gravity and centrifugal force.
- Recovering Balance with Arms: if we feel ourselves tipping over, we instinctively throw our arms out or forward. Moving our arm’s weight creates a “counter-torque” that helps pull our center of mass back over the middle of our skis.
Gravitational Torque (GT) is the “tipping force” that tries to pull our body toward the ground. Unlike the force of gravity (which just pulls us down the mountain), gravitational torque is the “destabilizing” component of gravity.
When standing upright on skis, gravity pulls downward, and the force passes directly through our Base of Support (BoS). There is no torque, however, the moment we angulate or lean to set an edge:
- The Center of Mass (CoM) shifts laterally, moving outside the vertical axis of the skis.
- A horizontal moment arm is created between the point of support (the ski edge) and the line of action of our weight. Imagine a straight line pointing down from the belly button (our weight). Now, look at where the ski touches the snow (our support). If those two lines aren’t perfectly lined up—for example, if we are leaning to the side—there is a horizontal gap between them. That gap is the “moment arm.“ Think of it like a wrench: the ski edge is the nut we are trying to turn. The gap (moment arm) is the handle of the wrench. Our weight is the hand pushing down on the handle. The wider that gap is, the harder gravity “pulls” to tip us over.
- This is critical for the Maintenance Torque because this gravitational torque is what tries to “defeat” our muscles. To avoid ending up on the ground, we must generate an Adductor Torque; by keeping our leg firm so our body does not collapse toward the inside of the arc.
- The Centrifugal Force, as opposing force, pushes us outward and compensates for the fall.
Simply put; to control our skiing, we adjust that horizontal gap (the moment arm) to change how much gravity “tips” or “rotates” us:
1.To Tip Over Faster (Starting a Turn)
When we want to start a turn, we move our body toward the inside of the curve. This increases the gap between our center of mass and our ski edges.
The result: the “wrench handle” gets longer, giving gravity more leverage to pull us down into the turn.
2. To Stop Tipping (Stability)
When we feel like we are falling over too far, we bring our body back over our skis. This shortens the gap.
The result: the “wrench handle” disappears. When our weight is directly over our edges, the gap is zero, and gravity stops trying to tip us. We become perfectly balanced.
3. Managing Speed and Pressure
- Longer gap: more “tipping force.” This is great for carving at high speeds because it helps us lean deep into the turn.
- Shorter gap: more “vertical pressure.” This is better for ice or slow maneuvers where we need our weight directly on top of the skis to keep them from sliding out.
In short: moving our body sideways grows or shrinks that “wrench handle,” allowing us to decide how much we want gravity to help us turn.
