If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Mechanics (Essentials) - Class 11th>Unit 9

Lesson 4: Why can a car not turn on ice?

# Introduction to centripetal force

Introduction to centripetal force, which accelerates an object toward the center of the circular path.

## Want to join the conversation?

• In which video had centrifugal force covered ?
• Centrifugal force does not exist. It is simply inertia resisting the change in direction.
• In this example, is the tension from the string that acts on the flaming ball the same as a centripetal force?
• 1. Why is the velocity of a spinning object must be tangent to a curved path?
2. Why is centripetal acceleration perpendicular to and towards the inside of a curved path?
• 1. Let us imagine the same example with a rotating tennis ball being held by you. Since it is circular motion, there will be a certain angular displacement of the ball per unit time. Finding the distance covered by the ball will simply give us the length of the arc travelled by the ball. Dividing that distance by the time taken will give us the speed of the ball around the centre (keep in mind that it is "speed" and not velocity as the distance covered by the ball is not linear but curving). If you were to let go of the chain while the ball was rotating, it is obvious that the ball will go flying off in one direction in a tangent to the original circular path it was taking. The ball will fly off tangentially with the same speed that it was rotating with. Since the speed of the ball is not in a linear direction, you can call it the velocity of the ball in a tangent: the tangential velocity. Hence, the speed of the ball moving in the circle can also be represented as its velocity in a tangent to the circle

2. If you are to make a straight moving body curve to a certain direction ,you must pull the body with some force from its side. As was explained, the speed of the ball can be represented as its tangential velocity. If you are to make this body curve towards the centre of the circle, there must be some force acting perpendicular to the direction of its tangential velocity to make it curve into a circle. This is proved by the fact that the radius is perpendicular to the tangent of a circle. So, to make a tangentially moving object curve towards the centre, you need a force to guide ,or pull, it towards a side. That is why the centrepetal force is towards the centre and the velocity of the body is tangential to the circle
• is centripetal force is the same as centripetal acceleration?
• No. When an object moves in a circular path, it is constantly accelerating because its velocity is constantly changing direction. This acceleration is what we refer to as centripetal acceleration because it points towards the center of the circle. By Newton's first law, if there is acceleration, there must be a net force. The net force always points in the same direction as the acceleration. Therefore, there must be a force acting on the object that points towards the center. It is this force that we refer to as a centripetal force. Note that a centripetal force is not a force in its own right, it is simply a type of force. If you attach a ball to a string and then whirl the ball around in a horizontal circle, the force of tension is the centripetal force. When the Earth orbits the sun, the force of gravity is the centripetal force. When a car negotiates a circular curve in the road, the centripetal force is static friction. Hope this helps!
• I was copying the drawing into my notes, but I did it from above, so just a circle, not a 3D oblong thing, and the acceleration vector for the second velocity (reddish vector connecting velocity vectors 1 and 2) didn't line up with the 2nd radius as it does here. So my acceleration vector does not point towards the center of the circle then when drawn in this fashion and it's bothering me. Could someone explain why?
• for the isosceles triangle formed by the two tangential velocity vectors, how could the velocity difference vector be perpendicular to one of the velocity vectors and co linear with the circle radius?
(1 vote)
• What does the magnitude of velocity mean?
(1 vote)
• According to Newton's 3rd law, there has to be a force that is preventing the ball from reaching the center. What is that force?
(1 vote)
• Centrifugal force. Or just Newton's First Law depending on what reference frame you look at it. The outward force of centrifugal force counters the centripetal force inwards, which prevents the ball from reaching the center. (The centripetal force is the tension).
(1 vote)
• Is a centripetal force the same as a perpendicular force?