Chapter 10 – Gravitation

Content Analysis: Concept of gravitation Law of gravitation and its importance Concept of free fall Acceleration due to gravity Motion of object under gravity Mass and weight Thrust and pressure Buoyancy and Archimedes principle Relative density

Tasks 10.1 Reasoning type 10.2 Reasoning type 10.3 Project based 10.4 Application type (numerical) 10.5 Application type (graphical

analysis) 10.6 Reasoning type 10.7 Group discussion

Learning outcomes

Learner is able to define: Gravitation Gravitational constant Acceleration due to gravity Mass Weight Thrust Pressure Buoyancy Relative density

Learner is able to distinguish between: Mass and weight Gravitational constant and acceleration due to gravity Thrust and pressure Density and relative density

Learner is able to understand and apply the following formulae: Law of gravitation Equations of motion under gravity Weight of object on different planets Pressure in fluids Relative density

Learner is able to apply the knowledge and understanding to solve problems based on experiments/activities/projects/data /figures.

TASK 10.1

Based on law of gravitation

Study the four situations given in the following diagrams. In which case is the

force of gravitation maximum?

m

m

m

2m

2m

2d

d

d/2m/4

d

m/44m

This question has been generated using the law of gravitation formulae and using the fact that m1m2/d2 is the same if the force between objects is same.

Therefore different diagrams show objects of different masses and varying distance between them. 1 mark for calculating force for each part and one for inference.

Assessment MethodAssessment Method

TASK 10.2

You and your classmate sitting next to you are at a distance of 50cm. According to law of gravitation both of you are attracting each other. Yet both of you remain sitting at the same position. Why so? Give reason for your answer.

Assessment Method This question is based on the

concept that the value of g is very small.

Therefore, the force acting between two objects in our daily life is very small and negligible. 1 mark for answer and one for reasoning

TASK 10.3 Theory Based Project

Visit a website of NASA/read any textbook of Physics and Collect and tabulate the value of mass and radii of different planets like Jupiter, Saturn, and Mercury. (i) Calculate the value of g in each case. (ii) Find the ratio of g on each of these planets with that on Earth.(iii) If your mass on Earth is 50kg, what is your weight on each of the above planets?

Assessment MethodThis question is based on formula for acceleration due to gravity and its understanding. It can be given as a home project work.

1 mark each for calculating ‘g’ on each planet. 1 mark each for finding the ratio in three cases. 1 mark each for finding the weight. The number of planets included in the above task

may be changed by the teacher.

TASK 10.4Problems based on equations of

motion under gravity

Your book gives three equations of motion under

gravity namely Eq .10.10, 10.11 and 10.12 on Pg

136 of NCERT book. Which one of these can be

generated using the other two? These equations

consist of 5 parameters namely u, v, t , a and s.

Which one of these should be constant for these

equations to be valid?

TASK 10.5Numerical Problems

(i) A ball is dropped from a height of 500m. Calculate the magnitude of displacement traveled by the ball in 2s, 4s, 6s, 8s and10s.

(ii) Plot a graph between distance and time.

(iii) What is the shape of the graph so obtained?

(iv) From the graph, find the distance traveled in 1st

second, 2nd second 4th second, 6th second and so on. Do these numbers form any mathematical pattern?

Assessment Method

Task 10.4 and 10.5 test understanding of derivation of equations between five parameters. This also tests that only two of them are independent equations and the third equation can be obtained using the other two.

Marks for each part can be suitably assigned.

TASK 10.6Based on - Thrust, Pressure, Buoyancy

and Archimedes’s principle

In figures (A) and (B), two beakers are filled with the same liquid. In Beaker (A), cube is completely immersed. In beaker (B), cylinder having same volume as that of the cube is fully immersed.

Which of the two objects experience greater buoyant force? Give reason for your answer.

Figure A Figure B

Assessment Method

This question is based on the concept that buoyant force is equal to the weight of the fluid displaced.1 mark for correct option and 1 mark for correct reason

TASK 10.7GROUP DISCUSSION

After the teacher has taught the concept of thrust, pressure and Buoyancy, students will be invited to distinguish between thrust, pressure and Buoyancy with suitable examples from daily life.

Assessment Method

The objective is that each student form the

concept of three terms correctly and is able to

understand the difference between the three.

The objective of group discussion should not

be value Judgment. Rather; this method

should be used to ensure that each student

attains a desired level of learning.