UNIT TEST 4

LESSON 7

• Friction: A force that resists the movement of an object.

• Traction: The friction between two objects that prevents them from sliding across each other.

• Lubricant: A substance that reduces friction between surfaces.

• Adhesion: The sticking together of two different materials.

• Gravity: The force that attracts objects toward each other, e.g., Earth’s gravity pulls objects toward it.

• Cohesion: The attraction between molecules or materials of the same type, causing them to stick together.

• Drag: The frictional force that slows down an object moving through air or water.

• Aerodynamics: The study of how an object’s shape affects its movement through air or water, aiming to reduce drag.

• Law of Universal Gravitation: The principle that states objects closer together exert a stronger gravitational pull than those farther apart.

• Centripetal Force: A force acting on a body moving in a circular path, directed toward the center.

• Terminal Velocity: The maximum speed an object reaches when falling through the atmosphere under the influence of gravity.

• Why do you slow down when you hit a dry patch on a water slide?

  • Because there is less friction when there is no water compared to when water is present, which aids in sliding.

• Why does a wet bar of soap slip and a dry one doesn’t?

  • The wet bar of soap has less friction compared to a dry one, making it slippery.

• Why is friction stronger on rough surfaces than on smooth surfaces?

  • Rough surfaces have more points of contact, leading to greater friction, while smooth surfaces provide less grip.

• Why does water decrease friction more than oil?

  • Water is less viscous than oil, allowing it to flow and reduce friction more effectively.

• What do we usually refer to when talking about adhesion?

  • Sticky substances are typically associated with adhesion.

• How does friction work when you rub your hands together?

  • The harder you rub, the more friction is created, which leads to heat (your hands feel warmer).

• Why do you need special boots for rocky hikes?

  • Special boots provide better grip, reducing the risk of slipping on rocky or uneven surfaces.

• What is Cohesion?

  • Cohesion refers to the attraction between molecules of the same material, causing them to stick together.

• What is traction?

  • Traction is the friction between two objects that prevents them from sliding against each other.

• If your car is stuck in the mud, is it better to push it out with a group of friends or put sticks and rocks under it?

  • It's better to put sticks and rocks under the car to provide extra grip and traction.

• What do we call sticky items?

  • Adhesives.

• If your car is stuck in the mud, why is it better to put sticks and rocks under it?

  • Putting sticks and rocks under the car gives it something to grip, helping it gain traction and avoid further slipping.

• How do ballerinas not slip while spinning?

  • The crew puts a sticky, soda-like substance on the stage to increase traction and prevent slipping.

• What is the Latin word for fluid?

  • "Fluo."

• Why does water slow you down underwater?

  • Water exerts friction against you as you move, which slows you down.

• What do American football players do when the ball is wet?

  • They use special gloves made from polymers that increase traction between the ball and their hands when catching it.

• Why is it difficult to keep your hand level when you hold it out of a car window?

  • Because of drag—the resistance created by air as you move the hand through it.

• Why are jets, submarines, fish, and birds shaped the way they are?

  • They are designed to reduce drag and optimize aerodynamics, making movement through air or water more efficient.

LESSON 8

Energy and Its Forms

• Energy is the ability to do work.

• Two main types of energy:

  • Kinetic Energy – Energy of motion (e.g., running, speaking, machines moving).

  • Potential Energy – Stored energy waiting to be used (e.g., a stretched rubber band, a battery, food before being eaten).

Law of Conservation of Energy

• Energy cannot be created or destroyed, only transferred or transformed (e.g., chemical energy in food turns into kinetic energy when you move).

Types of Energy

1. Chemical Energy – Stored in food, fuel, and batteries.

2. Thermal Energy (Heat Energy) – Energy from moving particles (e.g., fire, boiling water).

3. Mechanical Energy – Energy in moving objects (e.g., running, a rolling ball).

4. Electrical Energy – Energy from moving electrons (e.g., lightning, circuits).

5. Sound Energy – Energy that travels in waves through air or water.

6. Nuclear Energy – Energy stored in atoms, released through nuclear reactions.

Fossil Fuels

• Formed from buried plants and animals over thousands of years.

• Types:

  • Coal – Found worldwide, burned to produce electricity.

  • Oil – Used for fuel, plastics, and products like ink and crayons.

  • Natural Gas – Used for heating and cooking.

Renewable vs. Non-Renewable Energy

• Non-renewable energy: Fossil fuels and nuclear energy (take millions of years to form).

• Renewable energy: Continually replenished sources:

  • Solar Energy – Power from the sun, used in solar panels.

  • Wind Energy – Uses turbines to generate electricity.

  • Hydropower – Uses flowing water to turn turbines.

  • Geothermal Energy – Uses heat from inside the Earth.

  • Biofuels – Made from plants like corn and sugarcane.

  • Hydrogen Energy – Can be burned for energy, but hard to extract.

Issues with Energy Sources

• Fossil Fuels – Cause pollution but are currently the most widely used.

• Nuclear Energy – Produces a lot of power but creates radioactive waste.

• Wind Energy – No pollution but can harm birds and cause noise pollution.

• Solar Energy – Clean, but expensive and requires sunlight.

• Hydropower – Clean, but can harm aquatic ecosystems.