Solids, liquids, gases, plasmas, and Bose-Einstein condensates BEC are different states of matter that have different physical properties. Solids are often hard, liquids fill containers, and gases surround us in the air. Each of these states is also known as a phase.
Polar bears are in danger of extinction as well as many other species. There are 19 recognised subpopulations, and estimates place their numbers at about 20, to 25, Yet some claim that polar bear numbers have increased since the s and are now stable.
So what is the situation for this species? First of all, a few points need to be made about polar bear numbers: Nobody really knows how many bears there were in the s and s. Estimates then were based on anecdotal evidence provided by hunters or explorers and not by scientific surveys.
Polar bears are affected by several factors, including hunting, pollution and oil extraction.
Most notably, hunting, particularly following the introduction of snowmobiles, airplanes and ice breakers, led to a huge decline in certain subpopulations. The introduction of the International Agreement on the Conservation of Polar Bears inwhich restricted or even banned hunting in some circumstances, consequently resulted in an increase in polar bear numbers.
Not all subpopulations are affected to the same degree by climate change, and while some subpopulations are well studied, for others there is insufficient data to make broad statements about current and past numbers.
With this caveat in mind, what do the figures actually say? Figure 1 below compares the data for and Subpopulation status of polar bears for and Source: Polar Bear Specialist Group Both habitat degradation and over-harvesting are responsible for the decline in some subpopulations.
To understand why the IUCN and US Endangered Species Act consider polar bears to be at risk, it is important to look at how rising temperatures are likely to affect their habitat in the future.
Polar bears are highly specialised mammals which rely heavily on sea ice for food and other aspects of their life cycle. Satellite data show that Arctic sea ice has been decreasing for the past 30 years, and projections show that this trend will continue as temperatures carry on rising. The changes in sea ice affect polar bears in several ways: The early retreat of summer sea ice means that bears have less time to hunt and therefore less time to build up fat reserves.
The fragmentation and reduction in sea ice has several impacts. It forces the bears to swim longer distances, using up some of their fat reserves.
And it also forces the bears to spend more time on land, with increased interactions with humans potentially leading to higher mortality. A good example is the western Hudson Bay subpopulation, which is one of the best studied. Here, ice floe break-up is taking place earlier than 30 years ago, effectively reducing the feeding period by about three weeks.
In Alaska, there is evidence of increased cub mortality caused by a decline in sea ice.
Current analysis of subpopulations where data is sufficient clearly shows that those subpopulations are mainly in decline. Further habitat degradation will increase the threats to polar bears. Last updated on 22 July by pattimer.Science – Does Mass and Weight Affect Acceleration?
Essay Sample. Hypothesis: The heavier the car the slower (the more the mass the slower), the more weight(force. Speedy Science: How Does Acceleration Affect Distance? A fun physics project from Science Buddies.
Distance and Constant Acceleration, from Science Buddies. Learn About Mass & Weight. Share; Gravity. Pick up a book and then drop it on the floor. Why did it fall?
So when your mass changes, so does your weight! Science Words. Mass– the amount of matter than an object is made of. Mass does not change with gravity. Weight– the amount of gravity acting on (pulling down on). Emma Shields March 26, Hi David, Thanks for your comment.
The evidence linking obesity and cancer is tied to body fat, rather than muscle mass. BMI is the most common measure of body fatness.
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Forskolin is really effective for decreasing fat percentage in the body because it promotes the synthesis of cAMP. science investigates cause-and-effect relationships by seeking the mechanisms that underlie them.
The next concept—scale, proportion, and quantity—concerns the sizes of things and the mathematical relationships among disparate elements.