What is Motion?    A dictionary definition is:
"A change in the position of a body or system with respect to time."


  Isaac Newton, born in 1642 at Woolsthorp, Lincolnshire, in England defined three "Laws of Motion" that describe what happens when forces act on objects. And, after watching an apple fall from from a tree in his orchard, he defined his Law of Universal Gravitation.
  1. Newton's First Law of Motion: Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces acting on it.
  2. Newton's Second Law of Motion: Force equals mass times acceleration.
  3. Newton's Third Law of Motion: To every action force there is an equal and opposite reaction force.
  4. Newton's Law of Universal Gravitation: Between any two objects there is an attractive force proportional to the product of the two masses divided by the square of the distance between them.
  1. What sorts of things move? Planets rotate, people and other animals move from place to place, apples and other objects fall, mechanical devices twist, turn, slide and fly. This is a short list! Read on to find out more.

  2. What causes movement? Movement happens as a result of a force (energy) acting upon an object. The object can be as small as an atomic particle or as large as a planet or a star. No movement happens without the application of energy (force)

  3. What different forms of energy can cause movement? Identifying energy by the situations in which it exists we have:
  • nuclear energy (stored in atoms);
  • electrical energy (consisting of charged particles, electrons or protons);
  • chemical energy (stored in a molecule and released during chemical reaction),
  • mechanical energy (transmitted by a machine)
  • thermal energy (heat)
  • potential energy (the energy of a body as a result of its position or structure)
  • kinetic energy (the energy of a body that is in motion)
  4. Where does the energy that causes movement come from? Energy is stored in the substances that comprise our world and universe. Energy comes to Earth from the Sun and is used, stored or transmitted into space. Physicists believe that the amount of energy in the universe is a constant - it moves from place to place and is converted from one form into another but none is lost.

  5. What are some ways that electrical energy or heat energy move from place to place ? Convection, conduction and radiation
  5a) Convection. This is the name given to the transference of heat through gas or liquid media by the circulation of heated particles. For example: in nature there is rapid upward movement of air particles that have been heated by contact with surfaces on the Earth warmed by the sun. Electricity does not travel by convection.

  5b) Conduction. Heat moves (is transferred) fairly slowly by this method which involves heat energy being transferred molecule by molecule when a warm substance is in direct contact with a colder substance. Conduction is a typical method of transference of electrical energy and is rapid.

  5c) Radiation. This is a very rapid movement (transfer) of energy in the form of electromagnetic waves (radio waves, heat, light, X-rays, cosmic rays), and sound waves.



To understand how animals move we need to know some biology, some physics, and even some engineering concepts. The branch of science which brings these together to explain how animals move and work is called biomechanics.

  1. What is biomechanics? A dictionary definition might read like this:
"The application of the principles of mechanics to living systems."

For example, biomechanics would be used to figure out the stresses on bones as they are moved by the action of muscle force. Biomechanics is involved in animal locomotion on land, in the aerodynamics of bird flight, and in the fluid mechanics associated with swimming of fish.

  2. Why do animals move? Animals move from place to place to
a) Obtain food.
b) Find a mate
c) Find protection from the weather
d) Find a place to build a nest, burrow,
e) Escape predators

  3. What tissue powers movement in most animals? The force needed to initiate most animal movement is generated by muscles. In the case of locomotion in mammals, birds, amphibians, reptiles, and fish voluntary muscles acting against a framework of bones or cartilage power movement.

  4. What fuels the forces that cause movement in animals? Animal movement is fueled by the energy from food. The foods that can most readily be used to produce energy are carbohydrates and fats. The carbohydrates and fats are reduced to sugars and, in muscle cells, the sugars are converted by oxidation into carbon dioxide and water with release of energy. Some of this energy is in the form of heat, some is used to fuel other cellular processes, and some is used in the contraction of muscle fibers to cause movement.



  1. Do plants move from place to place under their own power? Land plants are anchored by their roots and so generally do not move from place to place of their own accord. Their above-ground parts (stems, leaves and flowers or fruits) are moved by wind or water; and aquatic plants may be moved bodily from place to place by the movement of the water in which they live.

  2. Do plant parts move other than as a result of an external force? Yes. Plant parts repond to certain stimuli such as light. For example when a plant stem is illuminated more brightly on one side it will often bend toward the light. This happens because plant hormones (auxins) accumulate on the more shaded side and cause the tissues on that side to grow more rapidly.

  3. How can plant reactions to stimuli be observed? The reactions are generally too slow to be observed by the human eye but observations over a period of time show the movement that has taken place. Time-lapse photography is one way of documenting such change.

  4. What disadvantage do plants experience as a result of being anchored in one place? Their inability to move bodily from one place to another influences plant distribution on the Earth's surface even though their fruits and seeds are usually dispersed some distance from a parent plant. More significantly perhaps, their fixed situation means that when the supply of water and nutrients in the soil becomes depleted they cannot move in search of a better situation.

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