Question

You lift your textbook and drop it onto a desk. Describe the energy transformations (from one form to another) that occur, moving backward in time from a moment after impact.

Short answer

Energy transforms from gravitational potential energy to kinetic energy, and then to sound and heat energy after impact.

Step-by-step solution

- Identify the final form of energy after impact

A moment after the textbook impacts the desk, the energy is primarily in the form of sound energy and heat energy due to the collision.

- Describe the energy transformation during impact

As the textbook hits the desk, its kinetic energy is transformed into sound energy and heat energy.

- Define the energy just before impact

Just before the textbook hits the desk, it has kinetic energy due to its motion.

- Explain the transformation from gravitational potential energy to kinetic energy

As the textbook falls, its gravitational potential energy is converted into kinetic energy.

- Identify the initial form of energy while holding the textbook

When the textbook is held in the air, it has gravitational potential energy.

Key concepts

kinetic energy

Kinetic energy is the energy that an object has due to its motion. When you drop your textbook, gravity accelerates it towards the desk. As it falls, it speeds up, and this increasing speed is due to its kinetic energy.

The formula for kinetic energy is \( KE = \frac{1}{2}mv^2 \), where \(m\) is the mass of the object and \(v\) is its velocity. As the textbook falls, its velocity increases, and so does its kinetic energy. This energy reaches its maximum value just before the textbook hits the desk.

Remember:

• Kinetic energy depends on both mass and speed.
• Larger objects or faster-moving objects have more kinetic energy.

gravitational potential energy

Gravitational potential energy (GPE) is the energy an object has due to its position in a gravitational field. When you lift a textbook and hold it in the air, it has gravitational potential energy. This energy is given by the formula \( GPE = mgh \), where \(m\) is the mass of the object, \(g\) is the acceleration due to gravity, and \(h\) is the height above the ground.

When you drop the textbook, its GPE transforms into kinetic energy as it falls. The higher the textbook is held, the more GPE it has, and the more kinetic energy it will gain as it falls.

• GPE depends on height, mass, and gravity.
• Higher positions or heavier objects have more gravitational potential energy.

heat energy

Heat energy, also known as thermal energy, is the energy that comes from the movement of particles within an object. When the textbook hits the desk, part of its kinetic energy is converted into heat energy.

The collision causes the particles in both the textbook and the desk to move more rapidly, increasing their thermal energy. This increase in heat might be too small to feel, but it's there. This transformation from kinetic to heat energy helps explain why objects get warmer when they collide.

• Heat energy increases with the movement of particles.
• Collisions often convert kinetic energy into heat energy.

sound energy

Sound energy is produced when an object vibrates, creating waves that travel through a medium like air. When the textbook hits the desk, the impact creates vibrations in the desk and the textbook, generating sound waves.

This is why you hear a noise when the textbook lands. The kinetic energy of the moving textbook is partly turned into sound energy. Sound energy is a form of mechanical energy and it dissipates quickly into the surrounding air.

• Sound energy is produced by vibrations.
• Impacts and collisions often create sound waves we can hear.