Questions about Forces and Tension

• vivekfan
In summary: However, once it is in flight, there is no longer a horizontal force from the bat. In summary, the tension in a string is zero when there is no acceleration. This does not mean that the tensions are necessarily equal, as they could have different magnitudes and opposite directions. For a baseball hit towards an outfield fence, the forces acting on it are gravity and the force from the bat while being hit, but once it is in flight, only gravity acts on the ball.
vivekfan

Homework Statement

This is a general question that I went over in class today. I'm not sure if I completely understand it. There is a block with a tension force pulling to the right and another tension force pulling to the left. Assume that it is in space (no gravity force or anything else). My teacher said that if there was no acceleration, there would be no tension in the string. Why wouldn't the tensions just equal each other? He said something about needing another force to balance the tensions, but why is the tension zero?

Also, another question.
If a baseball is hit and travels toward an outfield fence. What are the forces acting on the ball?

\
F=ma

The Attempt at a Solution

I thought that the tensions would just equal each other because they are the only two forces acting and the acceleration is zero. Why is this not true?

For the second question, I thought it would be obviously the downward force of gravity, but isn't there also a horizontal force because of the bat hitting the ball? I'm not sure if my reasoning is correct.

vivekfan said:

Homework Statement

This is a general question that I went over in class today. I'm not sure if I completely understand it. There is a block with a tension force pulling to the right and another tension force pulling to the left. Assume that it is in space (no gravity force or anything else). My teacher said that if there was no acceleration, there would be no tension in the string. Why wouldn't the tensions just equal each other? He said something about needing another force to balance the tensions, but why is the tension zero?

Also, another question.
If a baseball is hit and travels toward an outfield fence. What are the forces acting on the ball?

\
F=ma

The Attempt at a Solution

I thought that the tensions would just equal each other because they are the only two forces acting and the acceleration is zero. Why is this not true?
It is true. Perhaps your teacher meant there is no net force acting on the block; but the tensions could be any value, equal in magnitude and opposite in direction, as you have noted.
For the second question, I thought it would be obviously the downward force of gravity, but isn't there also a horizontal force because of the bat hitting the ball? I'm not sure if my reasoning is correct.
After the ball is hit and is in flight, only gravity acts on the ball. While it is being hit, then yes, you have a bat force acting as well (but not necessarily horizontal), which goes away after the ball leaves the bat.

I can provide some clarification and explanation for these questions.

Firstly, for the block with two equal tension forces pulling in opposite directions, if there is no acceleration, it means that the block is in a state of equilibrium. In this case, the forces are balanced, meaning that the net force on the block is zero. This is where your teacher's statement comes in - if there is no acceleration and the forces are balanced, then the tension in the string must also be zero. This is because tension is a force that is transmitted through a string or rope, and if there is no net force acting on the string, then there is no tension.

To understand this better, think about a tug-of-war game. If both teams are pulling with the same amount of force and there is no movement, then the tension in the rope is zero because the forces are balanced. As soon as one team starts pulling harder, the tension in the rope increases because there is now a net force acting on it.

For the second question about the baseball, you are correct in thinking that there are two forces acting on the ball - the downward force of gravity and the horizontal force from the bat. These two forces combine to give the ball a certain acceleration and trajectory. However, there are also other forces at play, such as air resistance and the force of impact with the fence.

Overall, it is important to understand that forces are not always equal and opposite, and that they can change depending on the situation and the presence of other forces. It is also important to consider all the forces acting on an object, not just the obvious ones, to fully understand its motion.

What is a force?

A force is a push or pull that causes an object to accelerate or change its motion. It is a vector quantity, which means it has both magnitude and direction.

What are the different types of forces?

There are several types of forces, including contact forces (such as friction and applied force) and non-contact forces (such as gravity and electromagnetic force). Forces can also be categorized as external (acting on an object from the outside) or internal (acting within an object).

What is tension?

Tension is a type of force that occurs when an object is pulled or stretched by another object or force. It is typically represented by a pulling force acting in opposite directions on an object, and can be found in situations such as ropes, strings, and cables.

How is tension related to other forces?

Tension is often related to other forces, such as weight and friction. For example, when an object is suspended by a rope, the tension force in the rope is equal to the weight of the object. In addition, tension can also be affected by the presence of other forces, such as when an object experiences both a weight force and a tension force.

How is tension calculated?

The amount of tension in a system can be calculated using Newton's laws of motion. To find the tension in a rope or cable, you would need to know the mass of the object being pulled, the acceleration due to gravity, and the angle at which the rope is being pulled. Other factors, such as friction and the presence of other forces, may also need to be taken into account.

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