Physical Science - Test 1 - 9th Grade RPC

1) Steps in the scientific method

  1. Ask a question / identify a problem

  2. Research background information

  3. Form a hypothesis (a testable prediction)

  4. Conduct an experiment

  5. Collect and analyze data

  6. Draw a conclusion

  7. Communicate results

  8. Repeat/modify if needed

2) Why do we use the scientific method? Why was it an improvement?

The scientific method is used because it provides a structured way to investigate questions and understand how the natural world works. It relies on evidence, testing, and observations instead of guesses or opinions.

Before the scientific method, many explanations were based on tradition, authority, or assumptions. The scientific method improved this because ideas could be tested and repeated by others, making scientific knowledge more reliable and accurate.

3) Compare accuracy and precision

Accuracy: How close a measurement is to the true or accepted value.

Example:

  • True value = 10 cm

  • Measurement = 9.9 cm → accurate

Precision: How close repeated measurements are to each other.

Example:

  • Measurements: 5.2 cm, 5.2 cm, 5.3 cm → precise

A measurement can be:

  • Accurate but not precise

  • Precise but not accurate

  • Both

  • Neither

4) Centripetal acceleration

Given:

  • Speed = 50 m/s

  • Radius = 100 m

Formula:

ac=v2ra_c = \frac{v^2}{r}ac​=rv2​ac=502100a_c = \frac{50^2}{100}ac​=100502​ac=2500100a_c = \frac{2500}{100}ac​=1002500​ac=25 m/s2a_c = 25 \text{ m/s}^2ac​=25 m/s2

Answer: 25 m/s²

5) Difference between vector and scalar

Scalar: Has only magnitude (size).

Examples:

  • Speed

  • Time

  • Temperature

  • Distance

Vector: Has magnitude and direction.

Examples:

  • Velocity

  • Force

  • Acceleration

  • Displacement

Example:

  • Scalar: 50 m/s

  • Vector: 50 m/s east

6) Rock dropped from cliff

Given:

  • Time = 2 seconds

  • Gravity = 9.8 m/s²

  • Initial velocity = 0

Formula:

d=12gt2d = \frac{1}{2}gt^2d=21​gt2d=12(9.8)(22)d = \frac{1}{2}(9.8)(2^2)d=21​(9.8)(22)d=4.9(4)d = 4.9(4)d=4.9(4)d=19.6md = 19.6md=19.6m

Answer: The cliff is about 19.6 meters high.

7) Newton’s 3 laws of motion

Newton’s First Law (Inertia)

An object stays at rest or in motion unless acted on by an outside force.

Newton’s Second Law

Force equals mass times acceleration.

F=maF = maF=ma

Newton’s Third Law

For every action force, there is an equal and opposite reaction force.

Example:

  • Rocket pushes gas downward → gas pushes rocket upward.

8) Horizontal projectile

Given:

  • Height = 10 m

  • Horizontal velocity = 100 m/s

First find falling time:

d=12gt2d=\frac12gt^2d=21​gt210=4.9t210=4.9t^210=4.9t2t2=2.04t^2=2.04t2=2.04t=1.43st=1.43st=1.43s

Now horizontal distance:

d=vtd=vtd=vtd=(100)(1.43)d=(100)(1.43)d=(100)(1.43)d=143md=143md=143m

Answer: About 143 meters

9) Forces on a box being pushed

Diagram:

        Normal Force
             ↑
             |
        ┌────────┐
        │  BOX   │ → Push force
        └────────┘
             |
             ↓
        Gravity
             
← Friction

Forces:


  • Gravity downward


  • Normal force upward


  • Applied push forward


  • Friction backward

10) Constant speed but still accelerating?

Acceleration can happen when direction changes, even if speed stays the same.

Example:

A car driving around a circular track at 50 m/s.

The speed stays constant, but the car is constantly changing direction, so it has centripetal acceleration.

Key formulas to memorize:

Newton’s 2nd law

F=maF=maF=ma

Centripetal acceleration

ac=v2ra_c=\frac{v^2}{r}ac​=rv2​

Free fall

d=12gt2d=\frac12gt^2d=21​gt2

Projectile distance

d=vtd=vtd=vt