# DK Science & Technology: Physics

Physics is the study of the forces, the energy, and the matter that make up the Universe and everything in it. APPLIED PHYSICS uses the discoveries of physics in medicine, engineering, and other practical situations.

## WHAT DO PHYSICISTS STUDY?

Physicists investigate what atoms are made of, how materials behave, and the forces that keep planets in orbit. They also study heat, light, sound, electricity, and magnetism. They try to discover the basic laws that matter and energy obey. Discoveries are usually written down as scientific EQUATIONS.

## WHAT ARE PHYSICAL PROPERTIES?

Physical properties are features that can be measured as numbers—length, weight, and volume, for example. Other physical properties include hardness, density, elasticity (how flexible a material is), conductivity (how well it conducts electricity or heat), and reflectivity (how much light it reflects).

## HOW DO PHYSICISTS WORK?

There are two main types of investigation in physics. Experimental physicists work in laboratories, designing experiments to measure physical properties and processes. Theoretical physicists work with ideas, equations, and models to uncover new laws of physics that can explain or predict the results of experiments.

## BIOGRAPHY: SIR ISAAC NEWTON English, 1642–1727

Isaac Newton made some of the most important scientific and mathematical discoveries of all time. His laws of motion and theories of gravity explain how all objects from atoms to planets move. His theories of optics (light) show that white light is made of a spectrum of colored light.

## EQUATIONS

An equation is a short way to write a scientific idea. For example, the density of a material is a measure of how tightly packed the matter inside it is. The equation density=mass/volume says that an object’s density is its mass divided by its volume.

### WHAT DO EQUATIONS TELL US?

An equation states that the amount to the left of the equals sign is the same as the amount on the right. Letters are used for physical properties—in the equation F=ma, F is force, and ma means mass (m) multiplied by acceleration (a). Some equations show the results of an experiment, and others show the predictions of a theory.

## APPLIED PHYSICS

Applied physicists use the basic laws of the physical world to design useful tools and techniques for many areas of science and technology, including medicine, astronomy, meteorology, materials science, and information technology.

### HOW IS PHYSICS USED IN MEDICINE?

Physics has been used to develop many valuable medical instruments and techniques. Scanners, X-ray machines, and laser surgery are based on discoveries made by physicists. So are heart monitors and radiation treatment for cancer.

## FIND OUT MORE

 Energy Forces Matter Measurements