Plate-loaded machines (such as the Smith machine) use standard barbell plates instead of captive stacks of plates. They combine a bar-end on which to hang the plates with a number of simple machines to convey the force to the user.
The plate-loaded machines will often have a very high mechanical advantage, due to the need to make room for large plates over a large range of motion following a path that causes them to converge at one end or the other. Also, the motion will generally not be vertical, and the net resistance is equal to the cosine of the angle at which it is moving relative to vertical.
For example, consider an incline press machine that is a single-lever machine that has the plates halfway up the lever from the handles to the fulcrum, and begins moving the plates at a 45-degree angle from vertical. The lever will provide a leverage advantage of 2:1, and the incline will have an advantage of 1:√2/2, for a net mechanical advantage of (4/√2):1 ≈ 2.8:1. Thus 50 kg (~491 N) of plates will apply to the user only an equaling weight of 18 kg or a force of ~174 N at the beginning of the motion.
On the other end of the spectrum may be a bent-over-row machine that is designed with the user's grip between the plates and the fulcrum. This amplifies the force needed by the user relative to the weight of the plates.
Read more about this topic: Weight Machine
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