Three States of Matter

Everything around us is made of matter. Matter is anything that has mass and takes up space. Scientists describe matter most often in three states: solid, liquid, and gas. In a solid, tiny particles are packed closely and vibrate in place. Solids keep their shape unless a force changes them. Ice, wood, and a metal spoon are solids. In a liquid, particles move more freely and slide past one another. Liquids take the shape of their container but keep the same volume. Water and juice are common liquids. In a gas, particles spread out and move quickly in all directions. Gases fill whatever space is available. Air is a mixture of gases we breathe, including oxygen and nitrogen. When matter is heated or cooled, it can change state. Ice melts into liquid water, and boiling water becomes water vapor, a gas. Understanding states of matter helps explain weather, cooking, and how materials behav…

Simple Machines Around Us

Simple machines help people do work by changing the size or direction of a force. There are six types: lever, wheel and axle, pulley, inclined plane, wedge, and screw. Complex machines, such as bicycles and can openers, combine several simple machines. A lever is a bar that pivots on a fulcrum. A seesaw is a lever. Pushing down on one end lifts the other. An inclined plane is a sloping surface—a ramp makes it easier to move heavy objects upward. A wedge is two inclined planes back to back; knives and axes are wedges that split or cut materials. A wheel and axle turns to reduce friction, like on a wagon or doorknob. A pulley uses a wheel with a rope to lift loads. Flagpoles and construction cranes use pulleys. A screw is an inclined plane wrapped around a cylinder; it holds wood together or lifts bottles from corks. Engineers study simple machines to design safer tools and buildings. N…