Question

Describe the interconversions of forms of energy occurring in these processes: (a) You throw a softball up into the air and catch it. (b) You switch on a flashlight. (c) You ride the ski lift to the top of the hill and then ski down. (d) You strike a match and let it burn completely.

Short answer

Energy conversions: (a) Chemical to kinetic to potential, back to kinetic; (b) Chemical to electrical to light and heat; (c) Electrical to potential to kinetic and thermal; (d) Chemical to thermal and light.

Step-by-step solution

Analyze the Energy Conversion in Throwing a Ball

When you throw a softball into the air, your muscles use chemical energy, which is converted into kinetic energy of the ball. As the ball rises, kinetic energy is converted into gravitational potential energy until it reaches its highest point. When descending, potential energy is converted back into kinetic energy. When you catch the ball, its kinetic energy is converted into thermal energy and sound energy as it impacts.

Understand Energy Conversion in a Flashlight

When you switch on a flashlight, the chemical energy stored in the batteries is converted into electrical energy. This electrical energy is then transformed into light energy and thermal energy as the bulb emits light and heat.

Examine Energy Conversion in Skiing

Riding the ski lift involves converting electrical energy into mechanical work to lift you to the top of the hill, increasing your gravitational potential energy. As you ski down, the gravitational potential energy is converted into kinetic energy. Some energy is also lost as thermal energy due to friction between the skis and snow.

Identify Energy Conversion in Burning a Match

Striking a match converts the mechanical energy of striking into thermal energy. This initial heat ignites the match, causing a chemical reaction that converts chemical energy in the match head into light energy and thermal energy as it burns.

Key concepts

Kinetic Energy

Kinetic energy is the energy of motion. When you throw a softball into the air, your muscles convert chemical energy into kinetic energy, propelling the ball upward. The formula for kinetic energy is given by \[ KE = \frac{1}{2} mv^2 \]where \( m \) is the mass of the object and \( v \) is its velocity. As the ball ascends, this kinetic energy gradually transforms into potential energy. However, as soon as it starts falling back, the potential energy reverts to kinetic energy, increasing the ball's speed. When you catch the ball, the kinetic energy is dispersed as thermal energy and sound through the impact with your hand.

Potential Energy

Potential energy is stored energy that depends on an object's position or state. In the context of a thrown softball, as it reaches the peak of its trajectory, its kinetic energy is maximally converted into gravitational potential energy. The potential energy in this scenario is calculated using:\[ PE = mgh \]where \( m \) is the mass, \( g \) is the acceleration due to gravity, and \( h \) is the height above the ground. This stored energy is what allows the ball to fall back under the influence of gravity, gradually transforming back into kinetic energy.

Thermal Energy

Thermal energy, or heat energy, is the total kinetic energy of particles within an object. It results from the random movements of molecules. When energy is converted from one form to another, some of it is often dissipated as thermal energy. For instance, when you catch a softball, the kinetic energy turns into thermal energy that slightly warms your hand, alongside other forms like sound energy.

• Flashlights also convert energy into thermal energy when the electrical energy flows through the filament, causing it to produce heat and light.
• Similarly, as you ski down a hill, the friction between skis and snow converts part of the potential energy into thermal energy, heating the snow slightly.

Chemical Energy

Chemical energy is stored in the bonds of chemical compounds and released during a chemical reaction. For example, our muscles store chemical energy, which is used to throw a ball or any physical activity.

• In the case of a flashlight, the chemical energy stored in its batteries is converted into electrical energy and then into light and heat as the flashlight is turned on.
• Burning a match is another clear example where chemical energy is converted into thermal and light energy. When you strike a match, it ignites a chemical reaction that releases stored energy as heat and light.

Each of these processes demonstrates the versatile role that chemical energy plays in everyday life.