SCIENCE
Summary & Practice Sheets
Grade 9- Physics
A Physics Toolkit Representing Motion Accelerated Motion Forces in one Dimension
Chapter 1
1. Methods of Science in Physics
Summary
Physics is the study of the physical world - matter and energy - and how they relate to each other.
The scientific method is a common approach to conduct an investigation. The common steps include:
- State the problem
- Research and gather information
- Form and test a hypothesis
- Analyze the data
- Draw conclusions
Scientists use models to represent ideas about things that are too difficult to investigate. They may be too small, for example, like subatomic particles, or too far away, like distant galaxies, or dangerous, such as the interior of nuclear reactors.
Scientists come up with theories to explain phenomena based on observations. These become scientific laws when they become a true general observation of nature.
Scientists don’t know everything and they make mistakes. This is why it is important for other scientists to peer review one another’s work.
2. Using Math to Express Concepts in Physics
Chapter 1
Summary
The International System of Units (SI) as a common system that scientists use worldwide. It has seven base units. All other units, like m/s, are derived.
Dimensional analysis is used to simplify calculations and derive the correct unit in a calculation.
Significant figures are used with scientific notation as the most effective way to express numbers that are too small or too large, such as the size of an atom or distance to a planet.
You have to solve a lot of problems in Physics and it is important to develop a strategy to avoid making mistakes along the way
1. Analyze : Identify the knowns and unknowns.
2. Solve : Identify the right equation and rearrange it for the unknown. You then add the values into the equation to solve it.
3. Evaluate : Check that the number, the sign (direction) and units make sense. The number of significant figures should correspond to input values.
3. Defining Accurate Measurements in Physics
Chapter 1
Summary
Every time that physicists take measurements, they have to record the degree of uncertainty in those measurements. Uncertainty gives a numerical value to the level of confidence in the result. This allows a comparison between different scientific studies.
Uncertainty in a measurement is +/- half of the smallestreadable value (like the millimeter gradation on a ruler).
Precision is how exact and repeatable a measurement is. Precision is determined by the sensitivity of the instrument used and the technique used to make the measurement. The figure to the right shows high precision.
Accuracy is how close a measurement is to the real value. The figure to the right shows high precision and high accuracy. Accuracy is affected by the calibration of an instrument. Two-point calibration is used to check the accuracy of the instrument.
The Global Positioning System (GPS) is a system of 24 satellites that orbit the Earth and send signals to a lot of receivers on Earth. It uses sensitive equipment and has many applications including satellite navigation in your car.
4. Using graphs in Physics
Chapter 1
Summary
Graphs are a visual tool to display experimental data and show patterns in data.
The independent variable (what is changed in an experiment) is plotted on the x-axis of a graph and the dependent variable (the change that is measured in an experiment in response to the independent variable) is plotted on the y-axis.
A line of best fit is drawn through the data points to show the general relationship between the independent and dependent variables. The graph on the right shows a linear relationship, expressed by y = mx + b, where m is the slope of the line and b is the intercept with the y-axis.
Nonlinear relationships include quadratic (y = ax2 + bx + c) and inverse relationships (y = ...)
A line of best fit can be used to predict data. Extrapolation is the extension of a line of best fit beyond the range of measurements. Care should be taken not to extrapolate too far. In this example, if too much mass is added to a spring it will eventually stretch in a nonlinear way.
Grade 9 Physics - Chapter 1: Methods of Science in Physics
QUESTIONS
Choose the correct answer:
1) Which of the following is an explanation supported by experimental results?
a) Scientific theory
b) Scientific method
c) Scientific law
d) Hypothesis
2) What is the field of science that studies mass and energy relationships?
a) Biology
b) Chemistry
c) Physics
d) Astronomy
3) In a closed system, "mass is always conserved” is an example of which of the following?
a) Scientific law
b) Scientific theory
c) Hypothesis
d) Model
4) Which is the way that an investigation is carried out?
a) Hypothesis
b) Scientific method
c) Scientific theory
d) Scientific law
5) An educated guess about a question that a scientist asks is called a ______.
a) model
b) scientific theory
c) scientific method
d) hypothesis
6) A bus is moving at a speed of 45 km/h. What is the speed of the bus in m/s?
a) 1.25×101 m/s
b) 1.5×103 m/s
c) 2.5 m/s
d) 1.5×102 m/s
7) Which type of relationship is shown by this graph?
a) Parabolic
b) Quadratic
c) Linear
d) Inverse
Think and Solve :
8) Re-order the following sentences to get a diagram about the scientific method.
Draw conclusions - Form a hypothesis - State the problem - Test the hypothesis - Gather information - Analyze data - Hypothesis is not supported - Hypothesis is supported.
9) Refer to the graph to answer the following questions.
1-What sort of relationship is shown in this graph?
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2- Is the slope of this graph positive or negative?
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3- What is the approximate position when the time is 4 s?
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4- Write the general equation for this graph (in symbols).
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10) Omar, Ahmad and Hamad measure the length of a box and each of them records the measurements :
If the length of the box equal (21.47 cm), answer the following :
1- Whose measurements are imprecise and inaccurate?
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2- Whose measurements are precise and inaccurate?
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3- Whose measurements are precise and accurate?
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