I have just done an experiment with a glider on an air track and applied a force to it. Its velocity increased very slightly and was wondering are there any reasons, other than friction, why the velocity could change during motion? Thanks I thought this but i dont know if its right "There is a logical explanation for why the velocity of the glider increased during motion for reasons other than friction. This is due to the air discharged by the air track, used to make the glider float and eliminate friction, disturbed the glider and possibly applied a small force to the glider, making the glider’s velocity increase by a small fraction. While there is force being applied by the air underneath the glider to keep it afloat, some of the air particles from the air that is discharged and is not covered by the glider, located on either side of the glider, may have applied this force. " Any suggestions would help.