Science Semester I Exam review – answer Key In science, experiments and investigations must be repeatable A prediction about a problem that can be tested is a hypothesis The factor being measured in an experiment is a variable The three branches of science are life, earth, physical When conducting an experiment, the last step is to draw conclusions A camera is an example of technology Scientists must be impartial and not base their conclusions on opinions To infer means to draw a conclusion based on something you observe Advertisements are designed to get you to buy a product or service. A collection of structures that relate to one another is a system The ability to use knowledge to decide if you agree with an explanation is called critical thinking The melting point is the temperature at which matter in a solid state changes to a liquid. Density is a measure of the mass of an object in a given volume A physical property is easily observed or measured without changing the object Chemical changes result in a new substance and cannot be reversed by physical means Solid, liquid, and gas are all examples of states of matter . Matter is anything that has mass and takes up space. In a physical change, the physical properties of a substance change, but the identity of the substance does not change. The boiling point is the temperature at which a substance in the liquid state becomes a gas. The law of conservation of mass states that the mass of what you end with is always the same as the mass of what you start with. It would probably be easier to ride a bike across a sidewalk than gravel or sand. The force that always acts opposite to the direction of motion of an object is called friction . According to Newton’s third law, forces always occur in equal but opposite pairs. Newton first described gravity while watching an apple falling. Velocity Is the speed of an object and its direction of motion. To calculate an average speed, you would use distance and time . Mass is NOT a force. The ability to cause change is energy. The average kinetic energy of the atoms in an object determines its temperature . Materials that do not transfer heat easily are insulators. At 0?C on the Celsius temperature scale, water freezes. An example of heat transfer by convection is the formation of air currents. The total amount of energy in the universe remains the same. An example of an exothermic reaction is the explosion of dynamite. The conversion of carbon dioxide and water to oxygen and sugar in photosynthesis is an example of an endothermic reaction. Radiation involves the transfer of energy by wave. If the amount of energy required to boil a pot of water were added to a swimming pool, the water in the pool would change very little. Exothermic reactions release energy. An object’s kinetic energy depends on its speed and mass. A book resting on top of a bookshelf has no kinetic energy. It does, however, have potential energy. As the mass of a moving object increases, its kinetic energy increases. What happens when two objects at different temperatures touch? Heat moves from the warmer object Heat flows easily in which material? conductor Waves can bend when they move from one medium to another. An electromagnetic wave DOES NOT need matter for energy transfer. In a mechanical transverse wave, matter moves at right angles to the wave direction. The speed of sound in water is greater than the speed of sound in air. A region of spread out particles in a compressional wave is called a rarefaction. Wave frequency is the number of waves passing a given point per second. In a compressional wave, matter moves back and forth in the same direction as the wave. The action of a wave bouncing off a surface is called reflection. Amplitude reflects the amount of energy in a wave. A wavelength is the distance between a point on one wave and the identical point on the next wave. The speed of waves can change when the waves move from one medium to another. A mechanical wave can travel only through matter. The action of a wave bending around a barrier is called - diffraction.