Oscillation and Periodic Motion in Physics

Oscillation and Periodic Motion in Physics Oscillation refers to the repeated back and forth movement of something between two positions or states. An oscillation can be a periodic motion that repeats itself in a regular cycle, such as a sine wave- a wave with perpetual motion as in the side-to-side swing of a pendulum, or the up-and-down motion of a spring with a weight. An oscillating movement occurs around an equilibrium point or mean value. It is also known as periodic motion. A single oscillation is a complete movement, whether up and down or side to side, over a period of time. Oscillators An oscillator is a device that exhibits motion around an equilibrium point. In a pendulum clock, there is a change from potential energy to kinetic energy with each swing. At the top of the swing, potential energy is at maximum, and that energy is converted to kinetic energy as it falls and is driven back up the other side. Now again at the top, kinetic energy has dropped to zero, and potential energy is high again, powering the return swing. The frequency of the swing is translated via gears to mark time. A pendulum will lose energy over time to friction if the clock isnt corrected by a spring. Modern timepieces use the vibrations of quartz and electronic oscillators, rather than the movement of pendulums. Oscillating Motion An oscillating motion in a mechanical system is swinging side to side. It can be translated into a rotary motion (turning around in a circle) by a peg-and-slot. Rotary motion can be changed to oscillating motion by the same method. Oscillating Systems An oscillating system is an object that moves back and forth, repeatedly returning to its initial state after a period of time. At the equilibrium point, no net forces are acting on the object. This is the point in the pendulum swing when its in a vertical position. A constant force or a restoring force acts on the object to produce the oscillating motion. Variables of Oscillation Amplitude is the maximum displacement from the equilibrium point. If a pendulum swings one centimeter from the equilibrium point before beginning its return journey, the amplitude of oscillation is one centimeter.Period is the time it takes for a complete round trip by the object, returning to its initial position. If a pendulum starts on the right and takes one second to travel all the way to the left and another second to return to the right, its period is two seconds. ​Period is usually measured in seconds.Frequency is the number of cycles per unit of time. Frequency equals one divided by the period. Frequency is measured in Hertz, or cycles per second. Simple Harmonic Motion The motion of a simple harmonic oscillating system- when the restoring force is directly proportional to that of the displacement and acts in the direction opposite to that of displacement- can be described using sine and cosine functions. An example is a weight attached to a spring. When the weight is at rest, its in equilibrium. If the weight is drawn down, theres a net restoring force on the mass (potential energy). When its released, it gains momentum (kinetic energy) and keeps moving beyond the equilibrium point, gaining potential energy (restoring force) that will drive it in oscillating down again. Sources and Further Reading Fitzpatrick, Richard. Oscillations and Waves: An Introduction, 2nd ed. Boca Raton: CRC Press, 2019.  Mittal, P.K. Oscillations, Waves and Acoustics. New Delhi, India: I.K. International Publishing House, 2010.

Abiotic and Biotic Stresses

Abiotic and Biotic Stresses What causes a plant to be stressed? As with humans, stresses can originate from the surrounding environment or, they can come from living organisms that can cause disease or damage. Water Stress One of the most important abiotic stresses affecting plants is water stress. A plant requires a certain amount of water for its optimal survival; too much water (flooding stress) can cause plant cells to swell and burst; whereas drought stress (too little water) can cause the plant to dry up, a condition called desiccation. Either condition can be deadly to the plant. Temperature Stress Temperature stresses can also wreak havoc on a plant. As with any living organism, a plant has an optimal temperature range at which it grows and performs best. If the temperature is too cold for the plant, it can lead to cold stress, also called chilling stress. Extreme forms of cold stress can lead to freezing stress. Cold temperatures can affect the amount and rate of uptake of water and nutrients, leading to cell desiccation and starvation. Under extremely cold conditions, the cell liquids can freeze outright, causing plant death. Hot weather can affect plants adversely, too. Intense heat can cause plant cell proteins to break down, a process called denaturation. Cell walls and membranes can also melt under extremely high temperatures, and the permeability of the membranes is affected. Other Abiotic Stresses Other abiotic stresses are less obvious but can be equally as lethal. In the end, most abiotic stresses affect the plant cells in the same manner as do water stress and temperature stress. Wind stress can either directly damage the plant through sheer force; or, the wind can affect the transpiration of water through the leaf stomata and cause desiccation. Direct burning of plants through wildfires will cause the cell structure to break down through melting or denaturation. In farming systems, the addition of agrochemicals such as fertilizers and pesticides, either in excess or in deficit, can also cause abiotic stress to the plant. The plant is affected by an imbalance of nutrition or via toxicity. High amounts of salt taken up by a plant can lead to cell desiccation, as elevated levels of salt outside a plant cell will cause water to leave the cell, a process called osmosis. Plant uptake of heavy metals can occur when plants grow in soils fertilized with improperly composted sewage sludge. High heavy metal content in plants can lead to complications with basic physiological and biochemical activities such as photosynthesis. Biotic Stresses Biotic stresses cause damage to plants via living organisms, including fungi, bacteria, insects, and weeds. Viruses, although they are not considered to be living organisms, also cause biotic stress to plants. Fungi cause more diseases in plants than any other biotic stress factor. Over 8,000 fungal species are known to cause plant disease. On the other hand, only about 14 bacterial genera cause economically important diseases in plants, according to an Ohio State University Extension publication. Not many plant pathogenic viruses exist, but they are serious enough to cause nearly as much crop damage worldwide as fungi, according to published estimates. Microorganisms can cause plant wilt, leaf spots, root rot, or seed damage. Insects can cause severe physical damage to plants, including the leaves, stem, bark, and flowers. Insects can also act as a vector of viruses and bacteria from infected plants to healthy plants. The method by which weeds, considered as unwanted and unprofitable plants, inhibit the growth of desirable plants such as crops or flowers is not by direct damage, but by competing with the desirable plants for space and nutrients. Because weeds grow quickly and produce an abundance of viable seed, they are often able to dominate environments more quickly than some desirable plants.