EXAMPLE 2: Dot and Spot 
Question 

Spot, the German Shepherd, is being walked by his best pal, Dot, the Siamese cat. Actually, Dot is pulling Spot across the ice rink,

and disturbing the neighbourhood hockey game. What are the forces acting on Spot? 


Hints 
The forces we discussed in the introduction were: 

1.gravity

2.normal

3.friction

4.pull or push by Dot 

Solution 

Since this is taking place on Earth, we can assume a gravitational force Fmg on Spot.

Also, because Spot is on the surface of the ice, the ice is exerting a normal force N on him. 

We assume that ice is frictionless, and so neither static friction nor kinetic friction acts on Spot (which he probably appreciates). 

The push/pull force may be misleading. While it is true that Spot is being pulled along by Dot, this is not the force acting on Spot. This is because Dot is actually pulling on the rope. The rope, in turn through its tension T, exerts a force on Spot. 

The FBD is


 

Explanation on FBDs

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