Grade 9 Physics Unit 4 : Force, Work, Energy, and Power

Unit 4 of your Grade 9 Physics course is called “Force, Work, Energy and Power.” In this unit, you will learn what a force is, how it moves things, and how work, energy, and power are used in everyday life and machines.

In Chapter 4.1, you will learn about the concept of force. A force is a push or pull on an object. You will learn that forces can start or stop motion, change the speed or direction of something, or change its shape.

Chapter 4.2 introduces Newton’s Laws of Motion. You will study three important rules that explain how and why objects move. These laws help us understand things like why seatbelts are needed in cars or why a ball keeps rolling until something stops it.

In Chapter 4.3, you will learn about friction. Friction is a force that tries to stop things from moving. You will learn how friction helps us walk without slipping, but also why it can make machines wear out.

Chapter 4.4 explains the concept of work in physics. In science, “work” means using force to move something. If nothing moves, no work is done—even if you are pushing very hard.

Chapter 4.5 teaches you about kinetic energy (the energy of moving things) and potential energy (stored energy, like in a stretched rubber band or a raised object). You will learn how energy can change from one form to another.

Finally, in Chapter 4.6, you will learn about power. Power means how fast work is done. You will study how to calculate power and understand why some machines are more powerful than others.