BY YILMA SHIFERAW
PHYSICS FOR GRADE 7:
Meaning of physics
The word ‘Physics’ comes from the Greek word meaning ‘nature’, introduced by the ancient scientist ‘Aristotle’. Man has always been fascinated by nature.
Physics is the study of matter, energy, and the interaction between them, but what that really means is that physics is about asking fundamental questions and trying to answer them by observing and experimenting.
Nature is complex and beautiful. Physics is an organized way of conversing with nature. Physicists ask; nature responds.
Physicists ask really big questions like:
•How did the universe begin?
•How will the universe change in the future?
•How does the Sun keep on shining?
•What are the basic building blocks of matter?
If you think these questions are fascinating, then you’ll like physics.
-Knowing the principles of physics enables us to comprehend, appreciate, and interact better with our environment. The occurrence of lightning and thunder, a rainbow, or tide can be explained by the principles and laws of physics.
How does physics relate to you?
Among the various disciplines of science, the only discipline which can be regarded as being most fundamental is physics. It has played a key role in the development of all other disciplines. For example,
-Physics in relation to Biological science: The optical microscopes developed in physics are extensively used in the study of biological samples.
-Physics in relation to chemistry: The study of structure of atoms, radioactivity, X-ray, diffraction, etc., in physics has enabled chemists to rearrange elements in the periodic table and to have a better understanding of chemical bonding and complex chemical structures.
-Physics in relation to astronomy: the giant astronomical telescopes and radio telescopes have enabled the astronomers to observe planets and other heavenly objects.
-Physics related to society and technology
“Any sort of technology which we uses in our daily life is related to Physics.”
Physics makes our lives more comfortable and enjoyable.
Did You Know
That the 2007 Nobel Prize in Physics was awarded for the science behind the magnetic hard drives in computers, iPods, and other kinds of electronic devices?
-Electricity is a gift of physics.
-Physics is applied in the construction of buildings, bridges, roads,and dams.
A]African Union Headquarters Addis Ababa, Ethiopia. [B]Abay bridge
[C] Gotera interchange ,addis abeba [D] Grand Ethiopian Renaissance Dam.
-Amusement park rides use physics laws to simulate danger, while the rides themselves are typically very safe.
The list is endless.
Physics is a field that can be used to explore many exciting phenomena, and its applications are vast.Almost any career you chose would benefit from your knowledge of physics and if you choose to learn more, perhaps one day you will be the one to discover something that changes the world!
Choose the best answer from the suggested options.
1.Which one of the following physicists was experimental physicist?
A.Albert Einstein B.Marie Curie C.Neil Bohr D. Charles Darwin
2.What is the first step in a scientific method?
A.Experiment B. Observation C. Conclusion D. Hypothesis
3.Which one of the followings has importance in trade and manufacturing?
A.Standardization of measuring units
B.Use of local measuring units
C.Use of human body parts as units of measurement
D.Conversion between different traditional units of measurement
4.Which of the following sets contains only fundamental physical quantities?
A. mass, volume, density B. area, speed, length
B. time, temperature, current D. force, luminous intensity, volume
5.Which of the following is a different physical quantity?
A. Force C. Area
B. Temperature D. Pressure
6.Which of the following is the SI unit of a fundamental quantity?
A. Newton B. Kilogram/cubic meter C. kilogram C. meter/second
7.Which is a scalar quantity?
A. Speed B. Displacement C. velocity D. acceleration
8.Which one of the following is the unit of a derived physical quantity?
A. candela B. meter C. ampere D. kg/m3
9.Which one of the following devices is NOT used to measure length?
A. Venire Caliper B. Spring balance C. Micro screw gauge D. Meter rule
10.What is the approximate length of one Ethiopian Birr?
A. 40.5 cm B. 1.35cm C. 4.05cm D. 13.5cm
11.A book is to be produced with pages of thickness 0.125 mm. If the book is to be exactly 2 cm thick, what is the maximum number of page it can contain?
A. 160 B.40 C.32 d.100
12. The unit best suited for measuring the length of a room in your home is ______
A. Km B. mm C.cm D. m
13. Which of the following is the most appropriate unit to specify the distance between two cities?
A. mm B. cm C. km D. m
14. It took a bus 3hours and 20 minutes to travel from one town to another. How much is this time in seconds?
A.12000 B. 10800 C.1200 D.1800
15.The SI unit of time is:
A. day B. hour C. minute D. second
16. In one day there are_________ minutes.
A.24 B.3600 C. 8640 D.1440
17.Almaz used 180g of sugar out of the 2kg contained in a packet what percent is left in the packet?
A. 91 B. 18 C. 80 D. 9
18. In one of the pans of a beam balance the mass 1 kg, 2kg, 500g and 250 g are placed. What should be the mass of body on the other pan if they are to be in equilibrium?
A. 3.75kg b.750g C.37.5g D. 570g
19. Which of the following physical quantities needs only magnitude to be described completely?
A. temperature B. velocity C. force D. acceleration
20.One metric ton is equal to
A. 907 kg B.1016 kg C. 100 kg D.1000 kg
ANSWER THE FOLLOWING QUESTIONS.
1. Define the following terms.
2.Explain the difference between
a.Distance and displacement
b.Average speed and average velocity.
c.Uniform motion and uniformly accelerated motion
3.Is the distance covered by a body always greater than the magnitude of the displacement?
4. Under what condition is displacement equal to the distance?
Choose the best answer from the suggested options.
1.Which of the following contains two vectors and a scalar?
A distance, acceleration, speed
B displacement, velocity, acceleration
C distance, mass, speed
D displacement, speed, velocity
2.Which one of the following is an example of rectilinear motion?
A.A ball thrown horizontally.
B.A stone thrown vertically upward
C.The motion of a pendulum
D.The motion of a pointer of a watch
3.Which of the following is an example of a rotary motion?
A. the motion of the moon around the earth
B. the motion of the ball thrown horizontally in to air
C. the motion of objects suspended on a spring
D. the motion of a pointer of a mechanical watch
Which one of the following motions represents vibratory motion?
A. Motion of a car along a curved road
B. Motion of gas particles in a confined bottle
C. Motion of the bob of a pendulum
D. A falling object
4. Suppose that an object travels from one point in space to another. Make a comparison between the displacement and the distance traveled.
A. The displacement is either greater than or equal to the distance traveled.
B. The displacement is always equal to the distance traveled.
C. The displacement is either less than or equal to the distance traveled.
D. The displacement can be either greater than, smaller than, or equal to the distance traveled.
5.In which one of the following cases will the distance covered and the magnitude of the displacement be the same?
(a) A girl climbs a spiral staircase.
(b) An athlete completes one lap in a race.
(c) A raindrop falls in still air.
(d) A passenger in a train travels from dire dewa to addis abeba.
6.A runner runs halfway around a circular path of radius 20 m .The magnitude of the displacement of the runner is
A. 62.8 m B. 40 m C. 20 m D. 125.6 m
8.One car travels 40. meters due east in 5.0 seconds, and a second car travels 64 meters due west in 8.0 seconds. During their periods of travel, the cars definitely had the same
a.total displacement B. average velocity C. average speed D. total distance
9.Which of the following properties of uniform rectilinear motion remains constant.
A. Displacement C. Time
B. Distance D. Velocity
10.A car moving in a straight road decreases its speed at a uniform rate from 45 to 15 in 10 seconds what is the acceleration of the car?
A. -6m/s2 B. -3m/s2 C. 3m/s2 D. 6m/s2
A. 4 m B. 12 m C. 24 m D. 36 m E. 60 m
12.The diagram represents the straight line motion of a car. Which of the following statements is true?
A. The car accelerates, stops, and reverses
B. The car accelerates at 6 m/s2 for the first 2 s
C. The car is moving for a total time of 12 s
D. The car decelerates at 12 m/s2 for the last 4 s
E. The car returns to its starting point when t = 9 s
WORK OUT [SHOW YOUR STEPS CLEARLY]
1.If you move 10 km north, 10 km East, and 10 km South,
a.What is the total distance you traveled?
b.What is your displacement?
2. An object is moving along a circular track of radius 2m with uniform speed. What is the ratio of the distance covered and displacement in half revolution?
3.A cyclist rides 3 km west and then turns around and rides 2 km east. (a) What is her displacement? (b) What distance does she ride? (c) What is the magnitude of her displacement?
4. You run from your house to a friend’s house that is 3 miles away. You then walk home.
a. What distance did you travel?
b. What was the displacement for the entire trip?
5.A car is driven 40 km due west, then 30 km due south. What is the magnitude of its displacement?
6. a) 35m/s =______ km/hr
b)45km/hr =_______ m/s
7. A runner runs around a circular track covers a distance of 200 m, ending in the spot where she started. If the entire trip takes her 50 seconds,
a. What is her average speed?
b. What is her average velocity?
8. A group of bike riders took a 4.0-hour trip. During the first 3.0 hours, they traveled a total of 50. Kilometers, but during the last hour they traveled only 10Kilometers. What was the group’s average speed for the entire trip?
9. A car moved 20 km East and 60 km West in 2 hours. What is its average velocity?
10. How far will a car travel in 15 min at 20 m/s?
11. A car travels with a uniform velocity of 20m/s for 8 seconds. How far would it travel in that time?
12. A jet flies at a constant velocity of 250m/s between cities 200,000meters apart. Find the time taken.
13. A cyclist takes 40 seconds to travel 200meters at constant velocity. At what velocity did he cycle?
14. Suppose you increase your walking speed from 1 m/s to 3 m/s in a period of 2 s. What is your acceleration?
14. A car slows down from 15 m/s to 10m/s in 2.5 seconds. What is its acceleration?
15.A car moving along a straight line at 40 m/s undergoes an acceleration of 3 m/s2. After 10 seconds its speed will be
16. How long does it take for a car to change its velocity from 10 m/s to 25 m/s if the acceleration is 5 m/S2?