Physical Science 8th grade (1).pdf

This makes the sea otter more effective in pushing

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force of water friction against the sea otter’s outstretched feet. This makes the sea otter more effective in pushing against the water to swim. Friction and forces are described by physics. Why a sea otter floats instead of sinking To find the shellfish they eat, sea otters dive down to the sea floor at the bottom of the kelp forest. Once they get a tasty clam or scallop, the otter swims back up to the surface and floats there to eat it. When it is floating, the sea otter is not swimming, yet it does not sink! A sea otter floats because its body is less dense than water. Density is a property of all matter, not just sea otters. Objects that are less dense (like the sea otter) float in liquids that are more dense (like water). Why living organisms need food to survive Like most living organisms, a sea otter eats to survive. What is eating? Why do living organisms need food? The answer is provided by chemistry (Figure 1.4). Living organisms are made of special chemicals known as proteins, fats and carbohydrates. The sea otter needs these chemicals to provide energy to keep its body warm. The otter also needs these chemicals to grow. The otter gets the chemicals it needs by eating shellfish. Biochemistry is a branch of chemistry that explores exactly how plants and animals use chemicals and energy.
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7 1.1 T HE P HYSICAL S CIENCE IN Y OUR L IFE C HAPTER 1: S TUDYING P HYSICS AND C HEMISTRY The sun is the source of energy for Earth The sun and energy Both living creatures and human technology derive virtually all of their energy from the sun. Without the Sun’s energy, Earth would be a cold icy place with a temperature of -273 degrees Celsius. As well as warming the planet, the Sun’s energy drives the entire food chain (Figure 1.5). Plants store the energy in carbohydrates, like sugar. Animals eat the plants to get energy. Other animals eat those animals for their energy. It all starts with the sun. Understanding what energy really is If energy is so important, what is it? The answer is slippery but essential to physics and chemistry. Energy measures the ability for things to change. Energy is exchanged when anything changes. Nothing changes when no energy is exchanged. For example, when you press its accelerator, the speed of a car changes. The change comes from the exchange of energy between the gasoline in the engine and the motion of the whole car. The sea otter’s body is warmer inside than the surrounding ocean water. Because the otter is warmer, heat energy flows from the otter into the ocean water. The otter needs a constant supply of energy from its food to replenish the energy exchanged with the water. Energy is such an important idea that you will find examples of energy in every single Unit of this book! Life on Mars and other planets A very important question in science today is whether there is life on other planets, such as Mars. Mars is farther from the sun than Earth. For this reason, Mars receives less energy from the sun than does Earth. In fact, the average temperature on Mars is well below the freezing point of water. Can life exist on Mars? Recent research suggests that can. Scientists have found
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