There are only two forces acting on a glider: an aerodynamic force and a gravitational force. The gravitational force is directed towards the center of the earth and is equal to the product of mass **m** and gravitational acceleration **g**.

The aerodynamic force is usually represented by its two components: the drag force **D** acting opposite to the direction of movement, and the lift force **L** perpendicular to it.

For a glider moving at constant altitude the lift force is equal to the gravitational force: **L = m * g** ... (equation 1)

There is no force opposing the drag force so according to Newton's second law there results an acceleration **a** resulting from the equation: **- D = m * a** ... (equation 2)

(The sign convention is positive for forces and accelerations in the direction of motion, negative in the opposite direction)

Combining equations (1) and (2) we get: **a / g = - D / L**

No need to discuss momentum or energy.

P.S. If you measure accelerations in kts/second, then g is about 19.05 kts/second

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Last edited by HazelNuts39; 25th Nov 2012 at 16:09.
Reason: P.S.
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