When lifting weights, it turns out the amount of force you need to lift them doesn't necessarily match the dumbbell's weight — in other words, if an object weighs 100 N, the amount of force you actually need to apply is probably not 100 N. Observe the diagram below:
When lifting weights, it turns out the amount of force you need to lift them doesn't necessarily match the dumbbell's weight — in other words, if an object weighs 100 N, the amount of force you actually need to apply is probably not 100 N. Observe the diagram below:
You can think of the bones in your arms as rods that rotate about an axis of rotation (your elbow) depending on the magnitude, direction and position of the forces being applied. So in order for your arm to lift the weight, the torque exerted by the bicep should be greater than or equal to the torques being applied by the bones' center of mass and the weight your hand is holding.
Notice how the bicep is connected to the arm bone (the radius) at a certain distance from the joint, and applies an upwards tension force (as the bicep contracts in order to lift objects).
Show how the magnitude of the tension force exerted by the biceps muscle can differ greatly from the magnitude of the weight.
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