# Static frictional force

• DKirby
In summary, the conversation discussed the physics behind a scene in Spiderman where the Green Goblin is standing on a bridge holding a cable attached to a cable car full of children. The force pulling on the Goblin was calculated to be 23,000lbs, and the discussion then turned to calculating the static friction between the Goblin and the bridge to see if he would be able to hold on. The calculated force needed to resist the cable pulling on the Goblin was 128lbs, assuming a horizontal pull. However, it was noted that cartoon characters can defy gravity under certain circumstances.

#### DKirby

I'm working on the physics behind a Scene in Spiderman, where the Green Goblin is standing on top of a bridge, holding a cable. along that cable is a cable car full of screaming little kids. I calculated the force pulling on the Goblin to be about 23,000lbs...and I'm sure even with his 800% strength increase he couldn't hold on to that.

So now I'm working on calculating the static friction between the Goblin and the bridge, to see if even if he was strong enough, if he would have enough friction to even stay put. What I have is

FsMAX (Max force that can be applied before object starts to move) = (Coefficient of static friction) * mass * gravity.

This comes out to be

FsMAX = (0.61)(95)(9.8) = 128 lbs

Where I'm guessing the Goblin's suit's material is aluminum, and the beam he's standing on his metal, and the Goblins weight + suit is 95kg.

My question is, is this calculation right? Or, would it take more than the 128lb force to start his feet moving because he's actually pulling back using force on the rope? And if that is the case, how would I go about finding the actual FsMAX?

Yep, good job Kirby. The force you calculated assumes a 0.61 coefficient of static friction, and that force is able to resist the cable pulling on the Green dude assuming the cable is pulling horizontally. Of course, if the cable is pulling at some downward angle, there is some increase in static friction because the downward angle gives the Goblin some additional downward force to augment his weight. But assuming a horizontal pull, you've got it figured out. Of course, cartoon characters can even resist gravity if the ground drops out from underneath them... so long as they don't realize it. Maybe some related phenomenon occurred to GG...

Your calculation for the maximum static frictional force is correct. However, there are a few other factors that could affect the actual force required for the Goblin to hold on to the bridge and the cable car.

Firstly, the coefficient of static friction may vary depending on the surface conditions of the bridge and the Goblin's suit. For example, if the bridge is wet or covered in debris, the coefficient of friction may decrease, making it harder for the Goblin to hold on.

Secondly, the force of the Goblin pulling on the cable may also affect the required static frictional force. If the Goblin is pulling with a significant force, it could increase the required frictional force to keep him in place.

Lastly, the Goblin's strength and grip also play a role. If his grip is not strong enough, he may not be able to hold on even if the maximum static frictional force is enough.

To get a more accurate calculation, you could consider these factors and also try to estimate the force the Goblin is pulling on the cable with. This would give you a better understanding of whether or not he would be able to hold on in this scenario.

## 1. What is static frictional force?

Static frictional force is a type of force that prevents an object from moving when a force is applied to it. It is the force that opposes the applied force and keeps the object in place.

## 2. What causes static frictional force?

Static frictional force is caused by the microscopic irregularities in the surfaces of two objects that are in contact. These irregularities create interlocking between the surfaces, resulting in a force that resists motion.

## 3. How is static frictional force different from kinetic frictional force?

Static frictional force acts on objects that are not moving, while kinetic frictional force acts on objects that are in motion. Static frictional force is usually greater than kinetic frictional force, making it harder to overcome.

## 4. How is static frictional force calculated?

The formula for calculating static frictional force is Fs = μsN, where Fs is the static frictional force, μs is the coefficient of static friction, and N is the normal force between the two objects.

## 5. How can static frictional force be reduced?

Static frictional force can be reduced by decreasing the coefficient of static friction or by decreasing the normal force between the two objects. Lubricants can also be used to reduce friction between surfaces, thereby reducing static frictional force.