1. Chapter 13 Section 1b: The Science of Rockets
How does a rocket work?
What is the main advantage of a multistage rocket?

2. Newton’s Third Law of Motion
If one object exerts a force on another object …
…then the second object exerts a force of equal strength in the opposite direction on the first object.
Ball
Head

3. Action-Reaction Pair
When the dog leaps, it pushes down on the ground (action force)
The ground pushes the dog into the air (reaction force)

4. Action-Reaction Pair
Action on the wall
When a skateboarder pushes against a wall (action force)
The wall pushes the skater in the opposite direction (reaction force)
motion
Reaction on the skater

5. How Do Rockets Work?
A rocket moves forward when gases shooting out the back of the rocket push it in the opposite direction.

6. Escaping Earth’s Gravity
In order for a rocket to move out of Earth’s gravity it must achieve a certain velocity called escape velocity.
In order for a rocket to go into orbit around the Earth it must achieve orbital velocity.
Which must be greater:orbital velocity or escape velocity?
How can scientists calculate the needed thrust to achieve the correct velocities?

7. Thrust Thrust is the reaction force that propels the rocket forward.
Thrust depends on the mass of the gases and the speed of the gases coming out the rocket engine. F=ma
To calculate the amount of thrust needed scientists use Newton’s second law.
Force (thrust) = mass x acceleration

8. Rocket Fuels Three types of rocket fuel are used
Solid fuel (fuel + oxidizer)
Liquid fuel (fuel + oxygen)
Electrically charged gas (ions)

9. Rocket Altitude
A rocket’s altitude is how high it is above the ground. Use the graph to answer the following questions about how a model rocket’s altitude changes over time.

10. Rocket Altitude Reading Graphs:
What two variables are being graphed? In what unit is each measured?
Altitude and time, meters and seconds

11. Rocket Altitude Reading Graphs:
What was the rocket’s altitude after 2 seconds? After 4 seconds?
About 65 meters; about 128 meters

12. Rocket Altitude Reading Graphs:
At what time did the rocket reach its greatest altitude?
6 seconds

13. Rocket Altitude Inferring:
Why do you think the rocket continued to rise after it ran out of fuel?
The rocket’s inertia caused it to continue to rise after its fuel ran out. Eventually friction caused the rocket to slow down and gravity caused it to fall

14. A Multistage Rocket
A typical multistage rocket has three stages. Each of the first two stages burns all of its fuel and then drops off. The next stage then takes over.

15. End of Section: The Science of Rockets