General Science Knowledge II

Motion and Forces

Motion is the ability to move or change position. Force is the influence on a system that causes a change in position or velocity. Motion is directly related to force. One cannot exist without the other. Both motion and force were described and explained by Sir Isaac Newton. Newton studied forces and motion and developed theories about them. In time, those theories were changed to law and are the foundation of physics classes around the world. Newton’s First Law states that an object at rest remains at rest and an object in motion maintains its velocity unless either object experiences an unbalanced force. We experience this law daily whenever we ride in a car. As the car comes to a stop, we move forward. Our muscles, seat belt and the friction between us and the seat stop our forward momentum. The opposite situation occurs when the car begins traveling again. The car will move forward and we will slide back. This is a daily demonstration of Newton’s first law.

Sample Problem

Paramedics lift a stretcher that is holding a person. The total mass of the stretcher and the person is 175 kg. The paramedics lift the stretcher at an upward acceleration of 0.425 m/s². What is the unbalanced force necessary to produce this acceleration of the person and the stretcher?

• List the given values:
  • f = ?
  • m = 175 kg
  • a = 0.452 m/s²
• Write the equation:
  • f = ma
• Plug in the known values:
  • f = 175 kg x 0.452 m/s2
  • f = 79.1 kg·m/s² = 79.1 N

Force is measured in newtons (N), named appropriately for Sir Isaac Newton. The Newton is the SI unit of force.

Newton’s Third Law states that for every action force, there is an equal and opposite reaction force. Consider playing sports. In baseball, a pitcher throws the ball to the hitter. The hitter swings and upon connection, sends the baseball flying away from the hitter. The force from the hitter swinging is transferred to the baseball which then changes direction to fly away from the hitter.

Electromagnetic Waves

Sir Isaac Newton may have been the founding father of forces and motion, however, there is more to physics than just force. Electromagnetic waves play a large role in physics and in the world around us. Right now you are using electromagnetic waves. Sitting at your computer you are using visible light. Listening to your radio utilizes radio waves and heating your food up quickly often takes microwaves. The electromagnetic spectrum is the full range of light at different frequencies and wavelengths. The electromagnetic spectrum consists of radio waves, microwaves, infrared waves, visible light, ultraviolet light, x-rays, and gamma rays.

• Radio waves are used for radio broadcasts, amateur radio, television, and mobile phones. Radio waves have a much longer wavelength than light waves. Radio waves cause electrons in metals to move and can generate electricity in a wire. Alternating currents in a copper wire generate electromagnetic waves and the electromagnetic waves in turn generate more alternating currents. These currents are radio waves.
• Microwaves have such a short wavelength that they are very easily absorbed by water. This is why they are used in microwave ovens. What happens is that when the water in your TV dinner absorbs the microwaves, the energy of the microwaves is converted into heat: it makes the water molecules vibrate faster.
• Infrared waves are radio/light waves that have a very short wavelength; their wavelength is longer than visible light. We cannot see Infra-red, but we can feel it warm our skin when we sit in the sun. Infra-red has a longer wavelength (less energy) than Red light.
• Visible light consists of the colors red, orange, yellow, green, blue, indigo, and violet. These are the colors and wavelengths that we see with our eyes.
• Ultraviolet waves have very high energy and very short wave lengths; shorter than visible light. We cannot see ultraviolet light, but we feel it on our skin when we have stayed in the sun too long without protection. Scientific investigation has proven that ultraviolet rays cause skin cancer. Due to the depleting ozone layer, more ultraviolet rays are hitting the earth now than used to.
• X-rays have so much energy and such a short wavelength that they can go right through you. However, they cannot get through bone as easily as they can get through muscle. This is because bones contain so much calcium.
• Gamma rays have very high energy and will even go through metals. So they can be used for finding tiny cracks in metals. Some radioactive materials produce gamma rays. Gamma rays and x-rays can both cause cancer, but they can also be used to destroy cancer cells; this is known as radiation therapy.

DNA

Deoxyribonucleic acid, commonly known as DNA, is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life. It is made up of organic molecules containing carbon, hydrogen, oxygen, nitrogen and phosphorus called nucleotides. The main role of DNA is the long term storage of information. It contains the instructions to construct other components of the cell, such as proteins and RNA molecules. The DNA segments that carry genetic information are called genes, but other DNA sequences have structural purpose, or are involved in regulating the expression of genetic information.

DNA has the shape of a twisted ladder known as a double helix. DNA consists of repeating nucleotides. The nucleotides are thymine, adenine, guanine and cytosine. Nucleotides always pair in a certain way:

Adenine → Thymine

Guanine → Cytosine

RNA

RNA serves as the template for translation of genes into proteins, transferring amino acids to the ribosome to form proteins, and also translating the transcript into proteins. RNA is the messenger. It carries the information from the DNA to ribosomes, where proteins are made.

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