What Causes a Box to Accelerate Down a Tilted Board?

In summary, when a board with a box on it is slowly tilted to a larger angle, the box will eventually "break loose" and accelerate down the board. This happens because the component of gravity acting parallel to the board becomes larger than the force of static friction, which causes the static friction to break and kinetic friction to take over. As kinetic friction is always smaller than static friction, there is a net force down the board that causes the box to accelerate.
  • #1
tnutty
326
1
When a board with a box on it is slowly tilted to larger and larger angle, common experience shows that the box will at some point "break loose" and start to accelerate down the board.

The box begins to slide once the component of gravity acting parallel to the board equals the force of static friction. Which of the following is the most general explanation for why the box accelerates down the board?

1 The force of kinetic friction is smaller than that of static friction, but remains the same.

2 Once the box is moving, is smaller than the force of static friction but larger than the force of kinetic friction.

3 Once the box is moving, is larger than the force of static friction.

4 When the box is stationary, equals the force of static friction, but once the box starts moving, the sliding reduces the normal force, which in turn reduces the friction.


I am thinking its 1.
 
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  • #2
Which of the following is the most general explanation for why the box accelerates down the board?

None explains acceleration.

It accelerates because gravity accelerates all objects in proportion to their mass...
 
  • #3
none is not a option
 
  • #4
Options 2, 3, and 4 aren't sentences and aren't understandable. Is a word missing?
 
  • #5
Mapes said:
Options 2, 3, and 4 aren't sentences and aren't understandable. Is a word missing?
Is this a ploy to pass native speakers?
 
  • #6
None of those made any sense to me.

This is why the box suddenly accelerates down the board:

The force of gravity is always acting on the box. Since the box is on a tilted board, one component of the gravitational force vector is pulling the board down the slope, and the other is into the board, determining the normal force. When the box is "sticking", it is because the static coefficient of friction between the two objects multiplied by the normal force is greater than the force pulling the box down the slope. As you tilt the board, the component of the gravitational force vector that goes toward pulling the box down the slope becomes bigger. At the same time, the component that determines the normal force becomes smaller. Eventually, the static coefficient of friction times the normal force will equal, and then be smaller than, the force pulling the box down the slope. The static friction will "break" and kinetic friction takes over. However, the kinetic coefficient of friction is always smaller than the static coefficient of friction, so the frictional force is not nearly enough to counter the force pulling it down the slope, so the net force is down the slope and the box accelerates.
 
  • #7
The reason it doesn't make any sense is probably because there is a term missing in every one. It should be:

The actual text is:

1. The force of kinetic friction is smaller than that of static friction, but F_g remains the same.
2. Once the box is moving, F_g is smaller than the force of static friction but larger than the force of kinetic friction.
3. Once the box is moving, F_g is larger than the force of static friction.
4. When the box is stationary, F_g equals the force of static friction, but once the box starts moving, the sliding reduces the normal force, which in turn reduces the friction.

---
At the point when the box finally does "break loose," you know that the component of the box's weight that is parallel to the board is equal to mu_s*n (i.e., this component of gravitational force on the box has just reached a magnitude such that the force of static friction, which has a maximum value of mu_s*n , can no longer oppose it.) For the box to then accelerate, there must be a net force on the box along the board...
 
  • #8
... and once static friction is broken, kinetic friction takes over, for which the coefficient is always smaller, so their is a net force, down the board, causing the box to accelerate.
 

Related to What Causes a Box to Accelerate Down a Tilted Board?

1. What is conceptual gravity?

Conceptual gravity is a term used to describe the fundamental understanding of gravity and its role in shaping the universe. It refers to the conceptual framework that scientists use to explain the behavior and effects of gravity.

2. How does gravity work?

Gravity is a force that exists between all objects with mass. The larger the mass of an object, the greater its gravitational pull. This force is what keeps planets in orbit around the sun and objects on Earth from floating away.

3. What is the difference between conceptual gravity and Newton's law of gravitation?

Conceptual gravity is a broader concept that encompasses all theories and ideas about gravity, including Newton’s law of gravitation. Newton’s law of gravitation is a specific mathematical equation that describes the force of gravity between two objects with mass.

4. How is gravity related to Einstein's theory of relativity?

Einstein's theory of relativity expanded upon Newton's law of gravitation by describing gravity as the curvature of space-time caused by the presence of mass. This theory has been proven to accurately explain the behavior of gravity in extreme conditions, such as near black holes.

5. What are some real-world applications of conceptual gravity?

Understanding conceptual gravity is crucial in many fields, including astronomy, physics, and engineering. It helps us understand the motion and interactions of celestial bodies, as well as the effects of gravity on Earth and other planets. It also plays a role in technological advancements, such as satellite navigation and space travel.

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