Evans SPH 3U1

Unit 2: Dynamics

Note 10: Tension and Internal Forces

Reference: Chapter 3.5

Tension:

• Uniform throughout the rope/string, can only pull
• Acts AWAY from the free body (Newton's 3rd law)
• Internal force which you can ignore when calculating acceleration (when treating it as one whole system)
• To find magnitude of tension, isolate ONE free body
Contact Force Between Two Objects Beside or On Top of Each Other:
• Internal force which you can ignore when calculating acceleration (when treating it as one whole system)
• Acts AWAY from the free body
• To find magnitude of contact force, isolate ONE free body

Example 1:
Three boxes are tied together in a line. You pull on the front one directly horizontally forward with a force of 20. N. The front box is 3.0 kg, the middle box is 2.0 kg and the last box is 1.0 kg. Assume that they are on a frictionless surface.
• a) Find th</b></b></b></b>e acceleration of the boxes
b) Find the magnitude of  tension between the last two boxes
c) Find the magnitude of tension between the first and second boxes.

Example 2:
See figure (c) in Sample Problem 1 pg 143. Now let us assume the mass on the right is 5.0 kg and the mass on the left is 2.0 kg.
a) Find the acceleration of the masses
b) Find the magnitude of tension in the string

Example 3:
Two boxes are in contact with each other and assume they are on a frictionless surface. The first box has a mass of 5.0 kg and the second box has a mass of 2.0 kg. You apple a foce of 150. N forward to the first box.
a) Find the acceleration of the boxes.
b) Find the magnitude of the contact force between the two boxes.

Pg 144 #1,2
Pg 146 #1,2
Pg 147 #3,4,6,7