Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Acceleration (velocity), in physics, the rate of change of velocity over time. An accelerating object is speeding up, slowing down, or changing the direction in which it is moving. Acceleration is a vector quantity—that is, it has both a magnitude and a direction. Acceleration describes both the magnitude of an object’s change in velocity, and the direction in which it is accelerating. Acceleration can thus involve changes of speed, changes of direction, or both. As acceleration is a rate of change of velocity over time and velocity is measured in meters per second (m/s), the units of measurement of acceleration are meters per second per second (m/s2).

Objects do not speed up, slow down, or change direction unless they are pushed in some way. Newton’s Second Law sums up this idea, stating that the acceleration of an object results from the application of a force. The acceleration (a) of an object with mass (m) produced by a given force (F) may be calculated using the equation F = ma. A larger force produces a greater acceleration; a larger mass results in a smaller acceleration given the same force.