Theories result from several repeated experiments.
Theories explain observations and hypotheses.
Theories may be revised over time.
Explanation:
Scientific theories are purely explanations into an observation and hypothesis. The are general binding explanations that have been developed from several tests.
- Theories are products of different stages of experiments in their own regard.
- For a theory to be accepted by the scientific community, its hypothesis statement must be:
- Testable
- Repeated
- Falsifiable
- Based on new evidence, a theory may be revised with time. One of such is the Dalton's atomic theory with a modern atomic theory version now.
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Pathogens are microorganisms that cause infectious diseases. Bacteria and viruses are the main pathogens in the world today.
The major problem that pathogen cause in society is that they are the agents of infection and disease.
An infection results when a pathogen invades the body and begins growing within a host. A disease results when tissue function is impaired due to an infection.
Due to diseases, affected people can not work which negatively affects the economy, and the sick may end up dying causing a lot of grief, and robbing society of a father, a mother or child.
The government has to put money aside for health care which would otherwise have been used for other things to help the society.
6. Since we are not sure if the person in the question is actively lifting the crate, we have to determine the downwards force of the crate due to gravity and compare it to the normal force.
F = ma
F = (15.3)(-9.8)
F = -150N
Since the downwards force of the crate is equivalent to the normal force, it means the person is applying no force in picking up the object. So to pick up a 150N object from scratch, you would have to exert more force than the weight of the object, so the answer is 294N.
7. Same idea as question 2.
First determine the weight of the object:
F = ma
F = (30)(-9.8)
F = -294N
The crate in question is not moving, so the magnitudes of the forces in the upwards and downwards direction has to equal to 0.
-294 + 150N + x = 0
x = 144N
So the person is exerting 144 N.
10. First find the force of block B to the right due to its acceleration:
F = ma
F = (24)(0.5)
F = 12N
So block B is moving 12N to the right relative to block A due to block A's movement to the left. However, block A is being applied a much greater force and is moving quicker to the left than block B is moving to the right of bock A. The force that is causing block B to experience the lower relative force to the right is because of the friction. To find the friction:
The sum of the forces in the leftward and rightward direction for block B must equal 12N.
75 - x = 12
x = 63N
So the force of friction of block A on block B is 63N to the left.
