Points to remember in Physics PART 7

Points to remember in Physics

PART 7

61. Acceleration is not equal to zero but speed is zero

If an object's speed is zero, it means the object is not moving. 

However, if the acceleration is not zero, it means that the object's velocity is changing, even though its speed is not changing. 

This can happen, for example, if an object is at rest and experiences a force that causes it to start moving, but then that force is removed and the object comes to a stop. During the time that the force is acting, the object's velocity is changing (accelerating), even though its speed remains zero. 

Another example could be an object moving in a circular path at a constant speed. Although the object's speed is constant, its velocity is changing because its direction is constantly changing, which requires an acceleration towards the center of the circular path.

62. No change in direction means speed is zero.

The statement "No change in direction means speed is zero" is not correct. In fact, it is the opposite of what is true.

If an object is not changing its direction, it means that it is moving in a straight line. If the object is moving in a straight line, its speed is not zero, but rather constant. 

Speed is defined as the rate at which an object changes its position, and it is a scalar quantity, which means it only has magnitude and no direction. 

If the object is moving in a straight line, its speed is the magnitude of its velocity vector, and its direction is the same as the direction of its motion.

Therefore, the statement "No change in direction means speed is zero" is not accurate. 

If there is no change in direction, it means that the object is moving in a straight line, and its speed is constant and non-zero.

63. Zero speed and a simultaneous velocity is not possible.

Similarly zero velocity and a simultaneous speed is not possible.

Correct that it is not possible to have zero speed and a simultaneous velocity, or zero velocity and a simultaneous speed. 

This is because speed and velocity are related to each other, and if one is zero, then the other must also be zero.

If an object has zero speed, it means that it is not changing its position with respect to time. In other words, the object is not moving. 

If an object is not moving, its velocity must also be zero because velocity includes both magnitude and direction. 

Therefore, it is not possible to have zero speed and a simultaneous velocity.

Similarly, if an object has zero velocity, it means that it is not changing its position in a specific direction. In other words, the object may be moving, but it is not moving in any particular direction. If an object is not moving in any particular direction, its speed must also be zero because speed only considers the magnitude of the velocity vector and ignores its direction. Therefore, it is not possible to have zero velocity and a simultaneous speed.

In summary, speed and velocity are related to each other, and if one is zero, then the other must also be zero.

63. When you say motion how the speed can be zero.

Motion refers to the change in position of an object over time. Therefore, if the speed of an object is zero, it is not in motion. 

However, it is important to note that an object can still be in motion even if its speed is not constant. 

For example, if an object is moving in a circular path, its speed may vary, but it is still considered to be in motion.

64. Magnitude of velocity is speed.

Magnitude of speed is magnitude of velocity.

From your point of view, You are correct that the magnitude of velocity is speed, and the magnitude of speed is the same as the magnitude of velocity.

Regarding your question, if there is no change in direction, it does not necessarily mean that the speed is zero. 

If an object is moving in a straight line, its velocity will have a constant magnitude and direction, and its speed will also be constant. 

However, if the object is not moving at all, then both its velocity and speed will be zero.

On the other hand, if an object is moving in a circular path, its direction is constantly changing, which means its velocity vector is also changing even if its speed remains constant. In this case, the object has non-zero velocity but zero acceleration in the direction perpendicular to the circular path.

65. To say speed is magnitude of velocity is same as saying velocity is magnitude of speed, this is a very confusing statement.

"To say speed is the magnitude of velocity is the same as saying velocity is the magnitude of speed, this is a very confusing statement."

This statement is incorrect and can be confusing. 

Speed is defined as the magnitude of velocity, but velocity is not defined as the magnitude of speed. 

Because Velocity is a vector quantity that includes both speed and direction, whereas speed is a scalar quantity that only includes magnitude. 

Therefore, it is not accurate to say that velocity is the magnitude of speed.

| Velocity | = speed

66. This condition is possible only when direction of velocity and direction of acceleration is same.

No, a body cannot have velocity and zero speed simultaneously. Velocity is a vector quantity that requires both magnitude and direction, whereas speed is a scalar quantity that only requires magnitude. If the speed of an object is zero, then the object is not moving at all, and therefore, its velocity is also zero.

However, it is possible for a body to have a non-zero velocity and zero acceleration. This occurs when the object is moving at a constant velocity in a straight line. In this case, the velocity does not change, and hence, the acceleration is zero.

Moreover, the direction of velocity and acceleration doesn't necessarily have to be the same for a body to have zero speed but non-zero acceleration. For example, an object can be moving in a circular path with a constant speed, and yet have an acceleration towards the center of the circle, known as centripetal acceleration. In this case, the direction of velocity and acceleration are perpendicular to each other, but the speed remains constant.

67. How does the speed of an object remain zero for motion in a frictionless surface with constant acceleration?

If an object is moving on a frictionless surface, there is no external force acting on the object to oppose its motion. Therefore, the object will continue to move at a constant speed in a straight line unless acted upon by an external force.

Now, if there is a constant acceleration acting on the object, the object will start to change its velocity. However, since there is no friction, there is no force to slow down the object's motion. As a result, the object will continue to move at a constant speed in a straight line, even though it is accelerating.

In other words, the acceleration only affects the direction of the object's motion, but not its speed. The speed of the object remains constant because there are no forces acting on the object to change its speed.

68. For uniform circular motion, speed is always constant, but velocity & acceleration varies due to change in direction... 

correct. 

In uniform circular motion, an object moves in a circle at a constant speed, but its velocity and acceleration are constantly changing due to the change in direction of motion. 

Velocity is a vector quantity that includes both speed and direction. In uniform circular motion, the speed of the object remains constant, but its direction changes continuously as it moves along the circular path. 

Therefore, the velocity of the object is not constant, and it changes at every point along the circle.

Acceleration is the rate of change of velocity. In uniform circular motion, the direction of velocity changes continuously, which means that the object is accelerating. This acceleration is called centripetal acceleration and is always directed towards the center of the circle. 

So, in conclusion, in uniform circular motion, the speed of the object is constant, but its velocity and acceleration are constantly changing due to the change in direction of motion.

69. Misconception: X-Rays were discovered in a scattering experiment.

X-rays were actually discovered during an experiment involving the emission of cathode rays. 

In 1895, German physicist Wilhelm Conrad Roentgen was conducting experiments with cathode ray tubes, which were vacuum tubes that emitted streams of electrons from a cathode to an anode. During one of these experiments, Roentgen noticed that a piece of fluorescent cardboard in his lab started to glow even though it was not in the path of the cathode rays. 

He realized that fluorescence was being caused by a new type of ray that was being emitted from the cathode ray tube. Roentgen called these rays "X-rays" because their nature was unknown at the time.

Roentgen conducted several experiments to study the properties of X-rays and found that they could penetrate through many different materials, including human tissue. This led to the development of X-ray imaging, which is now widely used in medicine for diagnostic purposes. 

So, X-rays were not discovered in a scattering experiment but rather in an experiment with cathode ray tubes.

70. Misconception: If the number of loops increases according to Faraday's law the magnetic field, electric field and voltage also increase.

According to Faraday's law of electromagnetic induction, the induced electromotive force (emf) in a conductor is directly proportional to the rate of change of magnetic flux through a surface enclosed by a conducting loop. The magnetic flux is the product of the magnetic field and the surface area, and it is measured in webers (Wb).

So, if the number of loops in a conductor increases, the surface area enclosed by the loops also increases. 

This means that the magnetic flux through the loops will increase, which will, in turn, increase the induced emf according to Faraday's law.

However, it's important to note that the magnetic field itself is not affected by the number of loops in a conductor. 

The magnetic field strength is determined by the current flowing through the conductor and the distance from the conductor. The voltage across the conductor also depends on the resistance of the conductor and the current flowing through it, in addition to the induced emf due to the changing magnetic field.