Pe Notes on Bimechanics
3A/B PE STUDIES – REVISION NOTES
Conservation of linear momentum when both objects are moving * In conservation of linear momentum the momentum of both objects before impact is not lost but remains the same for the combined momentum of both objects after impact.
Example
When playing snooker, once struck, the white “cue ball” will contain a certain amount of momentum. This is determined by its mass and how fast its travelling. When this ball makes contact with the black ball the total momentum of the two balls before and after collision will remain the same. Some of the momentum would have simply transferred from the white ball to the black ball. http://www.youtube.com/watch?v=qNou0xg3_cY Impulse-momentum relationship * Impulse (FXt) is the product of force and time. That is, how much force can be produced over a time interval. This impulse is then directly responsible for creating momentum (changing momentum from zero), changing momentum (increasing momentum in a slow jog to that required for a sprint) or stopping momentum (catching a ball). * The impulse needed to stop the momentum of a falling gymnast is constant; it is the time and therefore the peak force that may be altered. That is, the area under the impulse curve stays the same irrespective of whether you land in a foam pit or concrete – it is the shape of the curve that changes.
* Therefore the longer the force can be applied to an object and the greater the size of the force applied, the greater the object’s impulse! Coefficient of Restitution * The COR is the ratio of the velocities after compared with before an impact, and this value will change for different impact situations. * Rebound to the same height or with same velocity (e.g. collision during game of pool) = Coefficient of 1; perfectly elastic collision. * No rebound = Coefficient of 0; perfectly inelastic collision. * Rebound to a lesser height =Value >0 and <1; imperfectly inelastic
Conservation of linear momentum when both objects are moving * In conservation of linear momentum the momentum of both objects before impact is not lost but remains the same for the combined momentum of both objects after impact.
Example
When playing snooker, once struck, the white “cue ball” will contain a certain amount of momentum. This is determined by its mass and how fast its travelling. When this ball makes contact with the black ball the total momentum of the two balls before and after collision will remain the same. Some of the momentum would have simply transferred from the white ball to the black ball. http://www.youtube.com/watch?v=qNou0xg3_cY Impulse-momentum relationship * Impulse (FXt) is the product of force and time. That is, how much force can be produced over a time interval. This impulse is then directly responsible for creating momentum (changing momentum from zero), changing momentum (increasing momentum in a slow jog to that required for a sprint) or stopping momentum (catching a ball). * The impulse needed to stop the momentum of a falling gymnast is constant; it is the time and therefore the peak force that may be altered. That is, the area under the impulse curve stays the same irrespective of whether you land in a foam pit or concrete – it is the shape of the curve that changes.
* Therefore the longer the force can be applied to an object and the greater the size of the force applied, the greater the object’s impulse! Coefficient of Restitution * The COR is the ratio of the velocities after compared with before an impact, and this value will change for different impact situations. * Rebound to the same height or with same velocity (e.g. collision during game of pool) = Coefficient of 1; perfectly elastic collision. * No rebound = Coefficient of 0; perfectly inelastic collision. * Rebound to a lesser height =Value >0 and <1; imperfectly inelastic