Motion and Energy

Motion

What is Motion? Position is the location of an object. Motion is a change in position over time. Motion has two parts: distance and direction. Distance is how far the object moved. Positions and objects only make sense if you have a frame of reference. A frame of reference is a group of objects from which you can measure a position or motion.

What is Speed? Speed is how fast an object’s position changes over time. To calculate speed, divide the distance traveled by the time spent traveling. Velocity is the measurement that combines both the speed and direction of a moving object.

What is acceleration? Acceleration is the change in velocity over time for an object. An object accelerates when the object speeds up or slows down. When an object is going at a constant speed, the object is not accelerating. You also accelerate when you change direction even if the speed doesn’t change.

What is Momentum? Momentum is the product of mass multiplied by velocity. The more momentum an object has, the easier it is for that object to move other objects. When you want to change an objects velocity, you have to overcome inertia.

What is Momentum? Inertia is the tendency of any object to resist a change in motion or of a moving object to keep moving in a straight line. The more mass an object has, the more inertia it will have. The move inertia an object has, the harder it is to change its momentum.

Forces and Motion

What are forces? A force is any push or pull from one object to another. Units of force are the newton (N) and pound (lb). Force is represented in diagrams by arrows in the direction and strength of the force.

Gravity Gravity is a force of attraction, or pull between any two objects. Earth has gravity that causes things to fall back to Earth. Gravity is the force that keeps planets and moons in orbit. Gravity depends on the masses of the objects and the distance between them.

Gravity The more mass an object has, the more gravity will increase. The distance between objects will cause gravity to decrease.

What are friction and air resistance? Friction is a force that opposes the motion of one object moving past another. The amount of friction depends on the surfaces of two objects and how hard the objects are pushed together. Heat is created whenever there is friction. Shapes of objects influence how fast the object falls to Earth.

What are friction and air resistance? This is called drag force. Air slows objects that have broad, flat surfaces. If there is no air, all objects will fall at the same rate.

What is Newton’s First Law? An object at rest tends to stay at rest, and an object in constant motion tends to stay in motion, unless acted upon by an unbalanced force. When forces act on an object without changing its motion, they are called balanced forces. A force that causes an object to change its motion is called an unbalanced force.

Newton’s first law says that an object in motion could travel forever in a straight line as long as there was no friction, drag, or gravity.

What is Newton’s Second Law? The unbalanced force on an object is equal to the mass of the object multiplied by its acceleration: F = m x a. If the force increases, then the object will accelerate more. If the mass of an object increases, then the object’s acceleration will decrease.

What is Newton’s Third Law? All forces occur in pairs, and these two forces are equal in strength and opposite in direction. When one object pushes a second object, the second object pushes back on the first. The push of the first object on the second is called the action force. The push of the second object back on the first is called the reaction force.

Energy

What is energy? Energy is the ability to perform work or to change an object. Work is the measurement of the energy used to perform a task. Energy does not have to involve motion. Potential energy is the energy that is stored in the position or structure of an object.

There are many different forms of potential energy. Chemical potential energy is the energy in the links between atoms and molecules. A battery has chemical potential energy. Nuclear energy is also potential energy. Elastic potential energy is the energy stored by something that can stretch or compress. A stretched rubber band is an example of elastic potential energy.

Gravitational potential energy is the energy an object possesses due to its position above Earth’s surface. Gravitational potential energy increases as the object gets higher off the ground.

What is kinetic energy? Kinetic energy is the energy of a moving object. The faster the object is moving the more kinetic energy it has. The more mass an object has the more kinetic energy it will have. Heat, electricity, sound, and light energy are all forms of kinetic energy.

Some forms of energy can change the structure of objects rather than move them, but this is still work. Potential and kinetic energy can change back and forth easily. A roller coaster show how kinetic and potential energy change back and forth. At the top of the highest hill, the roller coaster has the most potential energy because it is the highest off the ground.

At the bottom of the highest hill, the roller coaster has the most kinetic energy because it is moving the fastest. As potential energy decreases, the kinetic energy increases.

How can energy change? Energy is transferred when it passes from one object to another. Energy is transferred from a bat to a baseball as it is hit. Energy is transformed when it changes from one form to another. Electrical energy can be transformed to light energy when you turn on a switch.

The law of conservation of energy says that energy cannot be created or destroyed. Sometimes energy does not work that is not productive. Heat is produced when a light is turned on but the heat is not what we want.

Heat

What is heat? Heat is thermal energy that flows between objects due to the difference in temperature. Heat moves from the object with the higher temperature to the object with a lower temperature. Temperature is the measurement of the average kinetic energy of particles in an object.

Heat will flow between two objects until they are the same temperature. We use a thermometer to measure temperature. Temperature is measured Celsius or Fahrenheit.

How does heat travel? Conduction is the passing of heat through a material while the material itself stays in place. Conduction works while two objects are touching, or in contact with one another. A metal spoon will get hot while it sits in a bowl of hot soup.

Convection is the flow of thermal energy through a liquid or gas, caused by hot parts rising and cool parts sinking. A pot of boiling water show convection. Water will heat up at the bottom of the pot and rise. When it rises it will cool off because it is not close to the heat source and sink back to the bottom.

Radiation is the transfer of energy through electromagnetic rays. An example of radiation is the sun warming the Earth’s surface. Hot objects radiate heat which you can feel but not see. Some animals have special organs to “see” infrared rays. And scientists have built special cameras to see infrared rays also.

Convection in Boiling Water

What is thermal conductivity? Thermal conductivity is the ability of a material to transfer heat. If a material conducts heat easily, it is a good thermal conductor. If a material conducts heat poorly, it is a good thermal insulator. Metals are good thermal conductors, and nonmetals are good thermal insulators.