When an arrow is fired from a bow I would expect from that there should be recoil pushing the bow backwards towards the archer. Yet references appear to contradict this, suggesting the bow wants to follow the arrow. Why?
• Your questioner is correct in his expectation that the recoil from firing an arrow should attempt to push the bow back towards the archer. And it does. When an arrow is fired from a bow the arrow gains momentum in the direction of flight and, because momentum is always conserved, the firing mechanism – the bow, the archer and even the earth on which the archer stands – must gain an equal amount of momentum in the opposite direction.
The reason for the perception that the recoil is in the direction of flight of the arrow is that, as the bow accelerates the drawstring and the arrow forward, the tips of the bow also move forward. They keep moving forward until the drawstring becomes straight and the tips and the drawstring come to a relatively abrupt halt. At this time, the bow exerts a forward force on the arm of the archer holding the bow – in other words, a recoil in the direction of flight.
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The recoil thus varies over time – a backwards recoil as the arrow and components of the bow accelerate forward, and a forward recoil as the components of the bow decelerate. Although the second component involves less change in momentum than the first, it occurs over a shorter time, so the forces are higher. This is probably why the forward component of the recoil is more readily perceived than the backward component.
Ian Vickers, Harrison, ACT, Australia
• In the case of a bow, the archer is part of the entire system and not separate from it. If the archer were wearing skates and standing on ice, he or she would recoil in a direction opposite to the trajectory of the arrow.
“If the archer were wearing skates, they would recoil in a direction opposite to the trajectory of the arrow”
A bow is traditionally made from wood, connected by a string. When the archer draws the bow, the tips bend back. When released, the tips of the bow relax back to their equilibrium position, in the same direction as the flight of the arrow.
Modern bows can be oriented vertically so that, when the bow is drawn, the tips are parallel with the ground and to each other. When the archer releases the string, more of the recoil happens in the vertical plane. This means the upward and downward recoil cancel out.
Mike Follows, Willenhall, West Midlands, UK