1. Normal force
The force that keeps one object from invading another object is called the normal force
“Normal” means “perpendicular”
You can determine the normal force by considering all forces that have components perpendicular to a surface

2. Problem: determine the normal force acting on a 5
Problem: determine the normal force acting on a 5.0 kg box sitting on a flat table.
Notice that this is equal in magnitude but opposite in direction to the Force due to gravity.

3. Problem: Now determine the normal force acting on a 5
Problem: Now determine the normal force acting on a 5.0 kg box sitting on a flat table.
F=16 N
40°

4. Problem: Now determine the normal force acting on a this 5
Problem: Now determine the normal force acting on a this 5.0 kg box sitting on a ramp at angle q=30o.
30o

5. Tension A pulling force. Generally exists in a rope, string, or cable.
Arises at the molecular level, when a rope, string, or cable resists being pulled apart.

6. Tension (static 2D)
The sum of the horizontal and vertical components of the tension are equal to zero if the system is not accelerating.
30o
45o 1 2 3
15 kg

7. Problem: Determine the tension in all three ropes.
15 kg
30o
45o 3 2 1
T1 = 147 N
T2 = 107 N
T3 = 131 N

8. Problem: A person weighs a fish using a spring scale that is attached to the ceiling of an elevator. What would the reading say the weight of the fish is relative to it’s true weight when the elevator is accelerating up and when it is accelerating down?
Therefore, because the tension will determine the scale’s reading it will read less than the actual weight of the fish when a is negative and more than the actual weight of the fish when a is positive.

9. Pulley problems
Pulley’s simply bend the coordinate system m1 m2

10. Sample problem: derive a formula for acceleration, assuming the table is frictionless.

11. Sample problem: derive a formula for acceleration, assuming the table is frictionless.q

12. q Sample problem: derive a formula for the tension T in the string. m1