# Classical mechanics - hunter and monkey - frame of reference

• ethanhunt
In summary, the conversation discusses the concept of frames of reference in physics, specifically in the scenario of a hunter aiming and shooting at a monkey jumping from a tree. The professor explains that in Newtonian mechanics, time is invariant between different frames, and therefore the time it takes for the bullet to hit the monkey is the same in both the monkey's accelerating frame and the class's static frame. The presence of gravity only alters the path of the objects, not the time taken. The concept of non-inertial frames affects the behavior of objects, making it difficult to predict using Newton's laws.
ethanhunt
Hi,

This might sound very basic and but i am just starting to learn physics.
I an lecture by prof. walter lewin, he descibes the hunter and monkey scenario. The monkey jumps from the tree as soon as the hunter aims and shoot his gun. the bullet hits the monkey anyway.
In calculating the time it takes the bullet to hit the monkey, he calculates from monkey's frame of reference and class's frame of reference to be same. He also states that the time is same irrespective of a moving frame (monkey's) and static frame (Class).

My doubt is, the monkey is accelerating with respect to the class. So the time and speed of bullet should not be the same for both as one is accelerating. From what i understand, an accelerating frame of reference will not produce same results as relative velocities will differ.
Please let me know your thoughts on this. Am i missing something?

Thanks
EthanHunt

What happens cannot depend on the frame of reference, whether accelerating or not. The monkey is either hit or not.

In Newtonian mechanics, time is invariant between different frames and so the time must also be the same in all reference frames. (This is different in relativity, but monkeys are not that fast.)

vanhees71
Hi Orodruin,

Thank you for the explanation. I tried measuring the time taken when the 2 are only along the vertical and it does work out. So as i understand the presence of gravity only alters the path of the objects. As such the time taken is the same else the monkey does not get hit.

I think i understand. the non inertial frame concept affects the Newton's laws as seen in the non inertial frame of reference. The behavior will not conform to the laws.
So in Newtonian mechanics, both frames measure the time at the same rate but the cause / effect will not make sense. We cannot predict the behavior correctly.

## 1. What is classical mechanics?

Classical mechanics is a branch of physics that studies the motion of objects and how forces affect their movement. It is based on the laws of motion and gravitation as described by Sir Isaac Newton.

## 2. How does the hunter and monkey thought experiment relate to classical mechanics?

The hunter and monkey thought experiment is a hypothetical scenario that helps us understand the concept of frame of reference in classical mechanics. It involves a hunter and a monkey on a tree, where the hunter shoots a dart at the monkey but misses due to the monkey's movement. This demonstrates the importance of considering the observer's perspective in determining the motion of objects.

## 3. What is a frame of reference in classical mechanics?

A frame of reference is a coordinate system used to describe the position and motion of objects. It is chosen by an observer and can be either stationary or moving. In the hunter and monkey thought experiment, the hunter and the monkey are each using their own frame of reference to describe the motion of the dart and the monkey, respectively.

## 4. How does the hunter and monkey thought experiment illustrate the principle of relativity?

The hunter and monkey thought experiment shows that the laws of classical mechanics are the same for all observers in uniform motion. This is known as the principle of relativity. In the scenario, both the hunter and the monkey are in motion, but the laws of motion still apply to both of them equally.

## 5. What is the significance of the hunter and monkey thought experiment in understanding the concept of inertia?

The hunter and monkey thought experiment demonstrates the concept of inertia, which is an object's tendency to resist changes in its state of motion. In the scenario, the monkey's movement causes the dart to miss its target, showing that the monkey's inertia affects the motion of the dart. This helps us understand how an object's inertia can impact its motion in different frames of reference.

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