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Class 8 Basic Science Chapter 2 Motion and Force Question Answer Notes
Class 8 Basic Science Chapter 2 Notes Kerala Syllabus Motion and Force Question Answer
Motion and Force Class 8 Questions and Answers Notes
Let’s Assess
Question 1.
A car starts from A and reaches B, which is 75 m away. The uniform speed of the car is 25 m/s. Another car with a uniform speed of 30 m/s starts from A and reaches B through C. Which car will reach the destination first?
Answer:
Speed = \(\frac{\text { distance travelled }}{\text { time taken }}\)
Car 1
Distance travelled_from A to B = 75 m
Speed of car 1 = 25 m/s
Time taken bv Car 1 = \(\frac{\text { Distance }}{\text { Speed }}\) = 75 ÷ 25 = 3 S
Car 2
Distance travelled from A to B through C = AC + CB = 50 + 70 = 120 m
Speed of car 2 = 30 m/s
Time taken by Car 2 = \(\frac{\text { Distance }}{\text { Speed }}\) = 120 ÷ 30 = 4 s
So Car 1 will reach the destination first because it takes less time.
Question 2.
A bus starts from C and reaches D in 7 s. If the uniform speed of the bus is 50 m/s, find the distance from C to D.
Answer:
Speed of the bus = 50 m/s
Time taken = 7 s
Speed = \(\frac{\text { distance travelled }}{\text { time taken }}\)
Distance travelled from C to D = Speed × Time = 50 × 7 = 350 m
Question 3.
How long will it take to hear thunder from 12000 m away? (The speed of sound is 340 m/s).
Answer:
Speed of sound = 340 m/s
Distance travelled by thunder = 12000 m
Speed = \(\frac{\text { distance travelled }}{\text { time taken }}\)
Time taken to hear thunder \(\frac{\text { Distance }}{\text { Speed }}\) = 12000 ÷ 340 = 35.29 s
Question 4.
Complete the puzzle given below:
Answer:
- Starts moving a stationary object
- Changes the direction of motion
- Changes the speed of a moving object
- Changes the shape of an object
- Changes the size of an object
Basic Science Class 8 Chapter 2 Question Answer Kerala Syllabus
Question 1.
Analyze the picture given above. What are the situations shown?
Answer:
- Child sitting on a moving giant wheel
- Person riding a horse
- Log of wood in a moving lorry
- Twig in the beak of a flying bird
- Earth in the solar system
- A book on a table
Question 2.
Tabulate the above situations that the objects change their position relative to the surroundings and those do not.
Answer:
| Objects changing position relative to surroundings | Objects not changing position relative to surroundings |
| • Child sitting on a moving giant wheel • Person riding a horse • Log of wood in a moving lorry • Twig in the beak of a flying bird • Earth in the solar system |
• A book on a table |
| Objects that change the position with respect to their surroundings are considered to be in motion, while those that do not change position are considered to be stationary. |
Question 3.
The above situations are given in the table below. Complete the table suitably by putting ✓ marks.
Answer:
From the table, we can infer that to determine whether an object is moving, we need to refer to another object. The object that is used as a reference is called the reference object.
| The object taken to determine the state of motion or the state of rest of a body is called the reference object. |
If an object changes its position relative to the reference object, it is said to be in motion, and if it does not change position, it is said to be stationary. Moving objects undergo a change in position.
Question 4.
The picture of a 400 m track is given below.
What will be the length of the path travelled by an athlete completing two rounds on this track?
Answer:
400 + 400 = 800 m
| Distance is the length of path travelled by an object. The SI unit of distance is metre. |
Odometre
An odometre records distance travelled by a vehicle in kilometre.
Question 5.
Since 1 km = 1000 m, calculate how far a vehicle has travelled so far, according to its odometer given above.
Answer:
1,44,969 km = 14,49,69,000 m
Question 6.
Figure 2.5 shows a railway track from A to F. Note down the distance traveled by the train upon reaching each place.
Answer:
| Place | Distance traveled |
| At A | 0 km |
| While reaching B | 60 km |
| While reaching C | 110 km |
| While reaching D | 150 km |
| While reaching E | 250 km |
| While reaching F | 320 km |
Question 7.
Bus A travelled 75 m in 5 seconds. Bus B travelled 112 m in 7 seconds. Which bus was faster?
Answer:
Speed of Bus A = \(\frac{\text { distance travelled }}{\text { time taken }}\) = \(\frac{75 m}{5 s}\) = 15 m/s
Speed of Bus B = \(\frac{\text { distance travelled }}{\text { time taken }}\) = \(\frac{112 m}{7 s}\) = 16 m/s
Bus B was faster.
Speedometer
Speedometre is the device that shows the speed of a vehicle.
Question 8.
The details of 3 children who participated in a 400 m running race in school sports meet are given in the table below. Can we find the fastest athlete among them.
Answer:
| Child | Distance | Time | Speed |
| A | 400 m | 180 s | \(\frac{400}{180}\) = 2.22 m/s |
| B | 400 m | 120 s | \(\frac{400}{120}\) = 3.33 m/s |
| C | 400 m | 400 s | \(\frac{400}{400}\) = 1 m/s |
Here, speed is the distance travelled in one second. The distance travelled in one second will not always be the same.
Question 9.
Look at the clock dial shown.
a) Complete the table based on the movement of the tip of the second hand (P in the figure). You can measure the distance between different points using a thread.
Answer:
| Change in position | Distance (cm) | Time (s) |
| From A to C | 10 | 10 |
| From C to E | 10 | 10 |
| From E to G | 10 | 10 |
| Change in position | Distance (cm) | Time (s) |
| From A to D | 15 | 15 |
| From D to G | 15 | 15 |
| From G to J | 15 | 15 |
b) What is the distance travelled in every 10 seconds?
Answer:
10 cm
c) What is the distance travelled in every 15 seconds?
Answer:
15 cm
If an object covers equal distances in equal time intervals, it is said to have uniform speed.
| If an object travels equal distance in equal intervals of time, it is in uniform speed. |
In our daily life, all movements are not in uniform speed.
Birds flying, humans walking, a ball rolling, etc., do not move with uniform speed. They move with nonuniform speed.
| If an object travels unequal distance in equal intervals of time, it is in non-uniform speed. |
Question 10.
We see vehicles ranging from slow-moving bicycles to high-speed cars on the roads. Road accidents due to excessive speed and carelessness are daily news. What can we do to avoid such road accidents? Discuss
Answer:
Road accidents caused by excessive speed and carelessness happen every day. To avoid such accidents, we : should always drive carefully and follow traffic rules. We must not rush or speed while driving. Wearing seat belts, paying attention while crossing the road, and avoiding distractions like using mobile phones while driving are also important. Being alert and responsible while on the road helps keep everyone safe.
Question 11.
Examine the figures.
Identify whether the force applied in each case is a contact or a non-contact force.
Answer:
| Situation | Force | Through Contact / Non-Contact |
| Mango falling downward | Earth’s Gravitational Force | Through Non-Contact |
| Leaves swaying in the wind | Force applied by wind | Through Contact |
| Magnet attracting a pin | Magnetic force | Through Non-Contact |
| Hammering a nail | Muscular force | Through Contact |
| Swimming | Muscular force | Through Contact |
| The force experienced when objects come into contact with each other is called contact force. The force effected when there is no contact with the object is called non-contact force. |
The standard unit of force is called the newton. It can be represented by the letter N. The capital letter is used because it is the first letter of the scientist’s name.
Question 12.
Where do we make use of friction in our life?
Answer:
Friction helps us walk, hold objects, drive, write, and stop vehicles. It provides grip and prevents slipping in everyday life.
Question 13.
Rub your palms together. Do you feel the warmth?
Answer:
When you rub your palms together, you can feel warmth. This happens because rubbing creates friction, which generates heat. Friction is the force that opposes the motion of two surfaces sliding over each other. So, the more you rub your palms, the more heat is produced, making your palms warm.
The same thing happens when striking a matchstick and lighting a lighter.
Advantages of friction
- Helps to hold objects firmly.
- Helps us in walking.
- Helps vehicles to move without slipping.
- Slows the fall and keeps the parachute open.
Question 14.
Is friction always beneficial?
Answer:
No, friction is not always beneficial. It has both advantages and disadvantages depending on the situation. Friction is helpful when we need to hold on or stop slipping. But in machines, too much friction is a problem because it wastes energy and makes parts wear out.
Disadvantages of friction
- Surfaces in contact wears out.
- Obstructs smooth movement of machine parts.
- Continuous friction between the bones during movement causes knee wear.
Question 15.
List some examples of lubricants.
Answer:
- Oil (such as motor oil, cooking oil)
- Grease (used in bicycles, machines)
- Wax (like bees wax)
- Soap solutions (used in some machinery)
- Graphite is a solid lubricant. It is commonly used as a lubricant between machine parts at high temperature.
Ball bearings seen in connection with tyres in vehicles and between hubs and the axles of ceiling fans and bicycles are used to reduce friction with the axle.
Airplanes and boats are made in special shapes to reduce friction. Smooth, streamlined designs help them move easily through air and water, making travel faster and easier by decreasing the resistance they face.
This method of reducing friction by changing the shape is called streamlining.
Question 16.
Write the various ways to reduce friction?
Answer:
- Use lubricants like oil, grease, or wax.
- Make objects streamlined.
- Use ball bearings in machines and vehicles.
Class 8 Basic Science Chapter 2 Question Answer Extended Activities
Question 1.
Prepare and present a seminar paper on the ways to reduce road accidents.
Answer:
Hints
Main Ways to Reduce Road Accidents
1. Follow Traffic Rules
- Obey speed limits
- Use signals and helmets
2. Improve Road Conditions
- Maintain roads properly
- Install clear signs
3. Raise Awareness
- Educate people about road safety
- Conduct awareness campaigns
4. Enforce Laws Strictly
- Penalties for Violations
- Regular checks for drunk driving
5. Use Technology
- Speed cameras
- Traffic lights and CCTV
6. Encourage Public Transport
• Less traffic, safer roads
7. Pedestrian Safety
- Crosswalks and footpaths
- Educate pedestrians
Question 2.
Prepare a science article on friction in daily life.
Answer:
- Friction is a force that opposes the motion of two surfaces sliding against each other. It is a common and important force we experience every day. Friction helps us in many activities, but sometimes it can also cause problems.
- Friction occurs when two surfaces come into contact and resist sliding. It acts in the opposite direction to movement. The amount of friction depends on the nature of the surfaces and how hard they press together.
Uses of Friction in Daily Life
- Walking and Running: Friction between shoes and the ground prevents slipping.
- Writing: Friction between pen and paper helps in writing.
- Driving: Friction between tyres and road helps in moving the vehicle without slipping.
- Climbing: Friction helps climbers grip rocks or walls.
Problems Caused by Friction
- Friction causes wear and tear of objects, like shoes or machine parts.
- It can slow down moving objects and waste energy.
How to Reduce Friction
- Use lubricants like oil or grease on machines.
- Smoothen surfaces to decrease friction.
- Use wheels and ball bearings.
Motion and Force Class 8 Notes
Class 8 Basic Science Motion and Force Notes Kerala Syllabus
- If an object changes its position relative to the reference object, it is said to be in motion, and if it does not change position, it is said to be stationary. Moving objects undergo a change in position.
- Distance is the length of path travelled by an object. The SI unit of distance is metre.
- An odometre records distance travelled by a vehicle in kilometre and a speedometre is the device that shows the speed of a vehicle in km/h.
- Speed is the distance travelled by an object in unit time. The SI unit of speed is m/s.
- If an object travels equal distance in equal intervals of time, it is in uniform speed.
- If an object travels unequal distance in equal intervals of time, it is in non-uniform speed.
- Force is a push or pull that changes the shape, size, volume, state of rest or state of motion of a body. The standard unit of force is called the newton.
INTRODUCTION
Understanding how objects move and interact is fundamental for the study of physics. This chapter introduces key concepts related to motion, including the difference between being at rest and in motion, and how distance and speed describe an object’s movement. We explore the forces that cause changes in motion, distinguishing between contact and non-contact forces, and examine the role of friction, a force that both opposes motion and its numerous practical applications in daily life. By grasping these fundamental ideas, we can better understand motion and force seen around us and learn how to control them to make our daily activities easier and safer.
STATE OF MOTION AND STATE OF REST
In our daily life we always engage in some activities. We move in various situations like running, playing and walking. A bird flying, a car running, leaves swaying in the wind – all these are different forms of motion.
SPEED
A photo finish picture of the 100 m race in the Olympics is given above. The athlete who completed 100 m in the least time would be the winner.
Experiment
Take a tall glass jar. Mark the top and bottom as A and B, respectively. Fill the glass jar with glycerin and drop a stone from the top. Start the stopwatch when the stone reaches A. Stop the watch when the stone reaches B.
Time taken for the stone to reach B = 5 s
Distance travelled = 30 cm
Distance travelled bv the stone in one second = \(\frac{30}{5}\) = 6 cm/s
| Speed is the distance travelled by an object in unit time. The SI unit of speed is m/s. Speed = \(\frac{\text { distance travelled }}{\text { time taken }}\) |
Although the SI unit of speed is m/s, the speed of vehicles is usually expressed in km/h.
Relation between km/h and m/s.
1 km/h = \(\frac{1000 m}{3600 s}\) = \(\frac{5}{18}\) m/s
FORCE
- Pulling a trolley
- Pushing a car
- Pushing a wall
- Pulling a table
We can see a push or a pull in all these situations. This is force. It is not only applied during pushing and pulling. Force can be applied in many ways, such as pressing, lifting, twisting, or even when objects attract each other (like gravity). Any action that causes a change in the motion or shape of an object involves applying force.
- Catching a ball
- Rolling dough to chapati
- Kicking a ball
- Hitting a cork
Here, we can see that force is applied to change the shape and direction of the object and to stop a moving object.
| Force is a push or pull that changes the shape, size, volume, state of rest or state of motion of a body. |
In all the situations shown above, force is applied through direct contact with the object. It is not necessary to have a direct contact in all the cases.
FRICTIONAL FORCE
You must have noticed that a ball rolling freely on the floor gradually comes to rest. The force responsible for this is called friction.
Let’s try an activity.
Take a wooden block and make one side smooth leaving the other rough. Slide its smooth surface down the inclined plane Then try to slide its rough side down the inclined plane.
Observation
More force is effected against the movement on a rough surface. This is frictional force. You can see that the speed decreases with the increase in friction.
| When a surface moves or tries to move over another surface, a parallel force is produced between them against their relative motion. This is frictional force. |
Activity
Slide a heavy box on a rough surface. Then move the same box on a trolley with tyres.
Observation
- The box moves faster on the trolley with tyres.
- The frictional force decreases in this case because rolling friction (or rolling resistance) is less than sliding friction.
Using tyres reduces the frictional force, making it easier and quicker to move the box.
| More friction occurs when sliding. This is called sliding friction. When using a trolley, the tyre rolls. This is rolling friction. Sliding friction is greater than rolling friction. |
WAYS TO REDUCE FRICTION
To understand the ways to reduce friction, we need to know the factors that influence it.
Activity
Take a wooden block, an ice block, and a rubber piece of the same mass. Allow them to slide down an inclined plane. The area in contact with the inclined surface should be equal in all cases.
Observations
- The rubber piece will slide slowly because of higher friction.
- The wooden block will slide faster than rubber but slower than ice.
- The ice block will slide the fastest because it has the least friction.
Nature of the surfaces in contact influence the frictional force
Experiment
Take some water in a glass jar and drop a round stone and a sharp-edged stone of equal mass into the water.
Observation
The round stone has a smooth shape, so it moves easily through water. It faces less friction and falls faster.
The sharp-edged stone has an uneven, rough shape. It faces more friction and falls slower.
From this, we can understand that the shape of the object affects friction.
Factors that affect friction
- Nature of surfaces in contact:
Rough surfaces create more friction than smooth surfaces. - Area of contact
Larger contact areas can increase friction.
We have seen that friction occurs when our palms are rubbed together. If oil is applied on the hands and rubbed together, they slip quickly. From this, it can be assumed thar friction is reduced when oil is applied.
| Substances that help to reduce friction between contacting surfaces are lubricants. |