course:fund_phy_exp:mech_lab

# Mechanics Laboratory -- Target hitting through collision

• Supervisor:Dr. Yongkang Le
• Location: Room 201-207， Henglong Physics Building
• This experiment is designed for the review of mechanics.
1. Projectile motion
2. Collision
3. Conservation law

In this experiment, you will be challenged to hit the target with a steel ball that is in projectile motion after being collided by another steel ball of the same mass at the bottom of its swing.

The followings are definitions of some related concepts:

• Projectile motion is the motion of an object moving through the air, subject to the acceleration of gravity. The object is called a projectile, and its path is called its trajectory.
• An conservative force is one, like gravity, for which work done by or against it depends only on the starting and ending points of a motion and not on the path taken.
• Conservation of mechanical energy: the total mechanical energy (i.e. sum of kinetic energy and potential energy) of a system that experiences only conservation forces is constatnt, can only changes forms among kinetic energy and various types of potential energy. Such a system is called a closed system.
• Conservation of momemtum: the total momemtum of any isolated system, with any numbers of bodies in it, is conserved. An isolated system is defined to be one for which the net external forces is zero.
• An elastic collision is one that conserves internal kinetic energy. Internal kinetic energy is the sum of the kinetic energies of the bodies in the system.
• An inelastic collision is one in which internal kinetic energy changes. This means the forces between colliding objects may remove or add internal kinetic energy.

For more details, please refer to your text book “College Physics”, especially §3.4, §6.4-6, and §7.3-6.

The experiment can be carried as follows:

1. Place the target-sheet in an appropriate position.
2. Place the projectile ball in its position.
3. Adjust the system so that after release, the ball will move in the vertical plane as decided by the projectile ball and the center of the target-sheet.
4. Measure the position of the center of the target-sheet. Calculate at which height the swing ball would be left free, so that the projectile ball will hit the center of the target-sheet.
5. Try the experiment once to verify your calculation.
6. If the center of the target-sheet is not hit, analyze the possible reason(s) and recalculate. Try again to verify the new calculation.
7. Procedure 6 may be repeated for several times until your “score” is better than 9th circle (inclusive).

Log your measured data, calculation, operation, phenomena and result in detail. Discuss the possible reasons which may result in energy lost in this experiment.

1. What is the main cause for energy lost in this experiment?
2. Write down the related equations you needed in this experiment. Specify the ranges of their application.
1. Paul Peter Urone, College Physics, Chinese Machine Press, Beijing 2002
2. Physics 8A – Fall 2000 Lab Manual, University of California at Berkley
3. 沈元华，陆申龙 基础物理实验 (Fundamental Physics Laboratory) 高等教育出版社 北京 2004 pp. 29-32
• course/fund_phy_exp/mech_lab.txt
• 最后更改: 2019/03/11 18:15
• 由 xiaole