UNIT 2: Kinetic & Potential Energy

Project Number: 2023-1-PL01-KA220-SCH-000164042

UNIT 2: Kinetic & Potential Energy

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Education and Culture Executive Agency (EACEA). Neither the European Union nor EACEA can be held responsible for them.

Introduction

• In this activity, you’ll explore kinetic and potential energy and the factors that affect them.

💡 We’ll see how energy changes form — from still to moving!

Source: freepik.com

Learning Outcomes

Sudent:Classifies energy as kinetic or potential. Understands that:

• Potential energy depends on mass and height.
• Kinetic energy depends on mass and speed.

Infers that energy is conserved when it changes form.

Source: freepik.com

What is Energy?

• Before understanding either form of energy, it’s vital to understand what energy really is.
• Energy is the ability to do work, which is when a force is applied to an object and it moves.

Source: freepik.com

Potential energy

1) Potential energy is one of the main types of energy in the universe. It’s fairly straightforward, although slightly difficult to grasp intuitively: It is a form of energy that has the potential to do work but is not actively doing work or applying any force on any other objects.

• Potential energy of an object is found in its position, not its motion. It is the energy of position.
• Potential Energy can be quantified as mass times gravity times height.

Source: freepik.com

• m is the mass in kilograms, g is the acceleration due to gravity (9.8 m / s² at the surface of the earth) and h is the height in meters. Potential energy is usually measured in units of Joules (J); one Joule is equal to 1 kg m² / s².
• When objects are displaced from positions of equilibrium, they gain energy that was stored in the objects before being knocked out of equilibrium by elastic rebound, gravity, or chemical reactions.
• This is best demonstrated in an object like an archer’s bow, which stores the energy that is created from pulling back the bowstring. The potential energy stored in the pullback is responsible for the energy that occurs upon release, which is known as kinetic energy.

Kinetic energy

• Understanding kinetic energy is intuitively easier because it’s more obvious that moving things have energy.
• Kinetic energy is created when potential energy is released, spurred into motion by gravity or elastic forces, among other catalysts. Kinetic energy is the energy of motion. When stored potential energy (energy of position) is transformed into motion, it becomes kinetic energy.

Kinetic energy

• Kinetic energy can be quantified as one half of the mass times the velocity squared. In SI units, the mass should be in kilograms (kg), and the velocity in meters per second (m/s).
• Kinetic energy has the same units as potential energy (kg m² / s²), and is measured using the unit Joule (J).

So why is there no gravitational acceleration in the kinetic energy formula? Doesn't gravity affect the motion of the object?

Source: freepik.com

Does Gravity Always Cause Motion? Think Again!

• Please take a moment and think about it.
• It actually seems quite logical, doesn't it? But it is not exactly true. Yes, gravity can be the cause of the motion of a free-falling object. But gravity may not be the cause of the motion in all cases.

Does Gravity Always Cause Motion? Think Again!

Consider, for example, a spaceship suspended in the vacuum of space in zero gravity. At rest, we can say that its kinetic energy is zero. But when it starts its engines and starts moving, it will have kinetic energy due to its speed.If we had added gravitational acceleration as a multiplier to the formula, we would have made the mistake of ignoring the kinetic energy of the spaceship since it is moving in zero gravity. So, we can state that gravity is not directly related to kinetic energy; it is just one of the possible components that are effective in the emergence of the velocity factor.

Source: freepik.com

Energy Transformation: From Potential to Kinetic

• You already know that energy is conserved and transferred within and between systems, not created or destroyed. Therefore, in a system where friction is neglected, the entire change in potential energy will be converted into kinetic energy.
• Now that we have learned the basics of kinetic and potential energy, we can solve a few problems using what we have learned.

Source: freepik.com

LEARNING ACTIVITY

• You can repeat the free fall activity designed in an augmented reality environment in different environments, with objects of different masses and by releasing them from different heights.

Scan the QR code on the right to explore the free fall simulation!

Designing Your Experiment:

Please answer the following questions using the simulation.

🧪 When designing your experiment, make sure to change only one variable at a time. Otherwise, it won’t be clear which factor caused the change in the results.

Practice Problems

a) Calculate the potential energy of an object with a mass of 15 kg at a height of 100 m, its kinetic energy at the moment of impact and how fast it will hit the surface. ……………………… POTENTIAL ENERGY: ……………………… KINETIC ENERGY: ……………………… VELOCITY:b) Calculate the potential energy of an object with a mass of 45 kg at a height of 100 m, its kinetic energy at the moment of impact and the speed at which it will hit the surface. ……………………… POTENTIAL ENERGY: ……………………… KINETIC ENERGY: ……………………… VELOCITY:

Practice Problems

c) Calculate the potential energy of an object with a mass of 15 kg at a height of 150 m, its kinetic energy at the moment of impact and the speed at which it will hit the surface. ……………………… POTENTIAL ENERGY: ……………………… KINETIC ENERGY: ……………………… VELOCITY:

Let’s Reflect on Energy Changes

What do you learn about kinetic and potential energy when you compare: cases ‘a’ and ‘b’? .................................................................................................................................................. .................................................................................................................................................. cases ‘a’ and ‘c’? .................................................................................................................................................. ..................................................................................................................................................

Now think deeper:

What would the results be if you did the same experiment on the Moon instead of Earth? 💬 Discuss with your peers! .................................................................................................................................................. ..................................................................................................................................................