Physics_Class VII

 Motion and Times

Q1. What is Motion?

Ans:- An object is said to be in motion (or moving) when its position changes with time. For example the position of Car changes with time, The Motion of Pendulum.

Q2. What are the Four types of Motion?

Ans:- The four types of Motion are : Rectilinear Motion, Circular Motion, Rotational Motion and periodic Motion.

Q3. Define Rectilinear Motion?

Ans:- Motion in straight line is called rectilinear motion. In other words, when an object moves along a straight line path it is called Rectilinear Motion. For example the motion of Bullock cart moving on a straight road, The march past of soldiers in a parade etc.

Q4. Define Circular Motion?

Ans:- A round path  having the shape of a circle is called circular path. When an object moves along a circular path, it is called circular Motion. For example the earth moves around the sun, Motion of a child in a merry-go-round etc.

Q5. Define Rotational Motion?

Ans:- When an object turns ( or spins) about a fixed axis it is called Rotational Motion. For example the earth turns round and round on its axis like a spinning top, The turning of blades of a fan etc.

Q6. Define periodic Motion?

Ans:- The Motion which repeats its self after regular intervals of time is called periodic Motion. The periodic Motion is also known as oscillatory motion. For example the pendulum of a clock, motion of a hammer in an electric bell etc.

Q7. What is speed?

Ans:- The distance moved by an object in a unit time is called speed of the object.

Speed = Distance Travelled /Time Taken

Example :- 100 Km/4 hrs = 25 Km per hour

Q8. Write the formula of distance travelled.

Ans:- One relation obtained by re arranging the speed formula is :

Distance travelled = Speed x Time Taken

Distance Travelled = 12 km x 2 Hrs=24 Kms

Q9. Write the formula of time taken.

Ans:- Another relation obtained by rearranging the speed formula is : 

Time taken = Distance travelled / Speed

Q10. What is speedometer?

Ans:- An instrument on a vehicle's dashboard which indicates the speed of the vehicle when it is running is called speedometer. The speedometer has the symbol Km/hour written on it's dial.

Q11. What is Odometer?

Ans:- Odometer is an instrument  for measuring the distance travelled by a vehicle.

Q12. Define uniform motion.

Ans:- An object moving along a straight line path is said to have uniform motion if it's speed remains constant.

Example:- The motion of a car running at a constant speed is an example of uniform motion.

Q13. Define non-uniform motion.

Ans:- An object moving along straight line path is said to have non-uniform motion if it's speed keeps changing.(It does not remains constant). The motion of a train starting form a railway station is an example of non-uniform motion.

Q14. What is distance-time graph?

A:- The motion of objects (like speed) can be represented in diagram form by drawing their distance-time graph. A distance-time graph shows how the distance travelled by a moving object changes with time.

Q15.  What is Sundial.

A Sundial is one of the earliest devices used for measuring time. A sundial measures time by the position of the shadow cast by the sun. We know that the sun rises in the east, appears to move in the sky during the day and finally sets in the west.

Q16. What is Sand Clock

Ans: Another early device for measuring time was the sand clock. Sand clock is also known as sand-glass or hour-glass. The sand clock uses the flow of sand (from one glass bulb to another) to measures time. The length of time taken by the sand to pass from one bulb of the sand clock to the other, gives a constant time interval.

HEAT

State similarities and differences between the laboratory thermometer and the clinical thermometer.

Similarities:

Both clinical and laboratory thermometers have long, narrow, uniform glass tubes.

The Bulbs of both the thermometers have mercury in them.

Differences

The temperature range of clinical thermometers is from 350C to 420C while that of laboratory thermometer is from -100C to 1100C.

Clinical thermometer is used to measure the temperature of a human body. However, laboratory thermometer cannot be used to measure the temperature of a human body.

The least count of both the thermometers differs.

Unlike clinical thermometer that can be tilted, laboratory thermometer is kept upright while reading the temperature values.

Give two examples each of conductors and insulators of heat.

Ans:-     Conductors of heat are:-a) Aluminium b) Iron

                Insulators of heat are:- a) Wood b) Plastic.

 Discuss why wearing more layers of clothing during winters keeps us warmer than wearing just one thick piece of clothing.

Answer:- During winters, we prefer wearing more layers of clothing than just one thick piece of clothing because air gets trapped in between the various clothing layers. Being a poor conductor of heat, air prevents heat loss from our body. Hence, layers of clothing keep us warmer than a single layer.

In places of hot climate it is advised that the outer walls of houses be painted white explain.

Ans:- In places of hot climate, it is advised to paint the outer walls of houses as white because a light colour such as white reflects back most of the heat that falls on it. Hence, a light colour tends to keep the house cool.