Full Idea
In place of Descartes's conservation of 'quantity of motion', Leibniz upheld both the conservation of linear momentum and the conservation of kinetic energy.
Gist of Idea
Leibniz upheld conservations of momentum and energy
Source
report of Gottfried Leibniz (Letters to Samuel Clarke [1716], 5th paper) by David Papineau - Thinking about Consciousness App 2
Book Reference
Papineau,David: 'Thinking about Consciousness' [OUP 2004], p.235
A Reaction
The point is that momentum involves velocity (which includes direction) rather than speed. Leibniz more or less invented the concept of 'energy' ('vis viva'). Papineau says these two leave no room for causation by mental substance.
Related Idea
Idea 20964 Descartes said there was conservation of 'quantity of motion' [Descartes, by Papineau]