When the ruler is broughı near the inetal knob, it repels electrons in the metal. Electrons move away froni the ruler and down the metal rod. The knob now has a positive charge. The thin pieces of metal foil at the bottom of the metal rod now have a negative charge.
Explanation:
physical exertion.
lack of physical activity.
lack of sleep.
being overweight or obese.
periods of emotional stress.
boredom.
grief.
taking certain medications, such as antidepressants or sedatives.
Many ecosystems and plants are damaged or destroyed when a volcano erupts.
Velocity, direction, or both at the same time.
