Table of contents
Kinetic energy is the energy of motion. Kinetic in Greek translates to "motion." The kinetic energy of an object depends on two factors: mass (m) and velocity (v). The mass of an object can be measured in kilograms (kg) and velocity of the object in meters per second(m/s).
The relationship between work and energy is visible when we compare the units of the two quantities. Since kinetic energy of an object is dependent upon mass (m) and velocity (v), the equation for kinetic energy is:
Work is dependent on mass, acceleration, and distance. The equation for work is:
When the units for both equations are added together the resulting units are kg m 2 s-2 which translated to the SI unit of energy called joule (J).
Kinetic Energy of a Bouncing Ball
For example, if we were to pick up a bouncing ball from the ground and bring it up to a height of 6 feet, we would have to apply a force over six feet to overcome the gravitational force pulling the ball down. The work done over the six feet is then stored in the ball in terms of potential energy, which can be simply defined as the potential to do work if the ball is released. When the ball is released it falls down, pulled by gravitational force. The potential energy the ball had when it was at rest at six feet gets converted into kinetic energy as the ball falls to the ground. Potential energy gets converted into kinetic energy because when the ball falls it is no longer at rest, but in motion. Kinetic energy is at its highest right before the ball hits the ground. Once the ball bounces off the ground, kinetic energy begins to decrease because the ball slows down. As the ball comes up after hitting the ground potential energy increases because the height of the ball increases.
Kinetic Energy of Atoms and Molecules
For a chemical reaction to occur there must be collisions between atoms or molecules to form a product. In order for the collisions to occur the atoms or molecules must have enough kinetic energy. The average kinetic energy of molecules can be measured in terms of temperature. Molecules with a high temperature have a greater kinetic energy than molecules with a low temperature. For example as the temperature of a gas begins to increase, the molecules of that solution begin to move faster, causing kinetic energy to increase.
Kinetic Energy of Chemical Reactions
Chemical reactions can either release energy (exothermic) or absorb energy (endothermic). During an exothermic reaction stored heat is released. When a chemical reaction releases energy, potential energy is converted into kinetic energy. When a chemical reaction absorbs energy, kinetic energy is converted into potential energy.
Relation Between Kinetic Energy and Thermal Energy
As discussed earlier, Kinetic energy is the energy of motion of all objects that can be defined by the equation. Thermal energy on the other hand is the kinetic energy of atoms and molecules of matter. We can find the thermal energy of atoms and molecules by measuring their temperature. As temperature increases, thermal energy of the atoms and molecules increases and as temperature decreases thermal energy of the atoms and molecules decreases.
Rotational Kinetic Energy
Rotational kinetic energy is similar to the kinetic energy of an object travelling in a straight line, but rotational kinetic energy is represented in a different context. The mass of a rotational object is moving in a circle rather than a straight line. Since the object is rotating its speed depends on the distance from the center of the object (radius) and angular speed. The equation for rotational kinetic energy is. I (moment of inertia) is equal to m (mass) x r2 (radius). For example a spinning wheel has a moment of interia of 7.2 and an angular speed of 10 m/s, its rotational kinetic energy would be equal to 360.
Kinetic Energy Equation
The equation for kinetic energy is:
Calculate the kinetic energy of a 40 kg object travelling 15 m/s.
Solution: mass= 40kg, velocity= 15 m/s, plug in these number into the kinetic energy equation
Calculate the kinetic energy of a 40 kg object travelling 30 m/s
As you double the velocity of an object its kinetic energy increases by four times, so the velocity of an object has a lot more impact on kinetic energy than the mass of an object.
Calculating the Kinetic Energy of Noble Gases
The kinetic energy of gases can be calculated using the equation:
where n is the moles of the gas, R is the gas constant 8.3145 J mole-1 K-1, and T is temperature in kelvin
Example: A 5g sample of He has a temperature of 100K, calculate the kinetic energy of the He atoms
Solution: convert 5g of He to moles of He 5g/ 4.00260g = 1.25 moles of He, then plug in 100k for T, and 8.3145 for R
This page viewed 43253 times