Understanding Forces in Static and Dynamic Systems

In summary: For part (c), the truck exerts a downward force on the chain while the float exerts an upward force, so the total force exerted on the chain is greater than the force exerted by the bumper on the rope. However, part (d) is a bit more complicated. The float is not attached to the chain at all, so the force exerted by the chain on it is zero. However, the force exerted by the bumper on the rope is the same as the force exerted by the rope on the bumper. So the total force exerted on the bumper by the chain and the force exerted by the bumper on the rope is greater than the force exerted by the rope on the float.
  • #1
PascalPanther
23
0
I am a bit confused, I thought I understood it, but the way the questions are worded seem to suggest I am wrong, which is usually a good indicator...
I keep putting things as equal, but it seems a bit of repetitive for everything to be equal. I am using Newton's third law for this.

1. Situation: there is an elevator hanging from a cable at rest.

a. Compare the force exerted by the cable on the elevator to that of the elevator on the cable.
They are equal. (1st law)

b. Compare the tension in the cable to the weight of the elevator.
The tension is equal to the mass of the elevator times the gravity.

c. The elevator begins accelerating upwards, compare the force exerted by the cable on the elevator, and vice versa.
I know that this is F = m (g+a) for the elevator. The F(net) needs to be upward. T-mg > 0. So it would mean the tension is greater than the downward force. However, the force exerted on the elevator by the cable and the force exerted on the cable by the elevator is still equal due to Newton's third law?

d. Compare the tension in the cable to the weight of the elevator.
Now, now I know that the tension is greater than the weight or it wouldn't accelerate.
-----
2. Similar question, a truck tries to pull a float (no movement), connected by a chain. Compare the force exerted by the bumper on the rope to the rope on the bumper, and rope on the float, to the float on the rope.
... They are all equal ...
The float begins to move...
... Aren't they all still equal? Rope to bumper, bumper to rope; float to rope, rope to float
 
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  • #2
If they all had the same mass they would be equal. The way you have it seems right.
 
  • #3
For part (a), the force of the cable on the elevator and the force of the elevator on the cable are equal and opposite because of Newton's 3rd law. His 1st law concludes that the force of the cable on the elevator upward is equal to the force of gravity on the elevator downward (its weight) , as per your response to part (b).
 

What are Newton's three laws of motion?

Newton's first law states that an object will remain at rest or in motion with a constant velocity unless acted upon by an external force. Newton's second law states that the force applied to an object is equal to its mass multiplied by its acceleration. Newton's third law states that for every action, there is an equal and opposite reaction.

How do Newton's laws apply to everyday life?

Newton's laws can be seen in everyday life in various ways. For example, the first law can be seen when a car comes to a stop when the brakes are applied. The second law can be seen when a person pushes a shopping cart - the harder they push, the faster it goes. The third law can be seen when a rocket is launched into space - the force of the rocket pushing down on the ground is equal to the force of the ground pushing the rocket up.

What is the difference between mass and weight according to Newton's laws?

Mass is a measure of the amount of matter in an object, while weight is a measure of the force of gravity acting on an object. According to Newton's second law, an object's weight (force of gravity) is directly proportional to its mass and the acceleration due to gravity. Therefore, an object with a greater mass will have a greater weight.

How do Newton's laws relate to the concept of inertia?

Newton's first law, also known as the law of inertia, states that an object will remain at rest or in motion with a constant velocity unless acted upon by an external force. Inertia is the tendency of an object to resist changes in its motion. This means that an object with a greater mass will have a greater inertia and will require more force to change its state of motion.

What is the significance of Newton's laws in physics?

Newton's laws are the foundation of classical mechanics and are essential in understanding the motion of objects. They provide a framework for predicting and explaining the behavior of objects in motion. They are also used in many engineering applications, such as designing cars, planes, and buildings.

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