1. Aim: How do we apply newton’s 2nd law to THINGS MOVING UPWARDS AND DOWNWARDS?

2. Weight
Fg = mg Fg=weight m=mass g=acceleration due to gravity Ex: Calculate the weight of a 12 kg toy cart.
What is the difference between weight and mass?

3. Normal Force
The normal force is the force that the ground exerts on an object in a direction perpendicular to its surface.

4. Ex 1
Bob with mass of 80 kg stands at rest on the surface of the earth. What is the normal force acting on Bob?

5. Normal force and its applications to elevators
A person of 70 kg stands on a scale in an elevator.
Calculate the force that the scale reads when the elevator is:
At rest
Accelerating upwards at 2m/s2
Accelerating downwards at 2 m/s2

6. More elevator problems
An elevator descending comes to a stop with an acceleration of 4 m/s2. If your mass is 70 kg and you are standing on a scale in the elevator, what does the scale read as the elevator is stopping?
967 N

7. Tension force
The tension force is the force that the rope exerts on the object.

8. Ex.3 – Tension Force
A vertical tension force is exerted on a 5kg object near the surface of the earth.
Find the acceleration of the object if
T=5N
T=10 N
T= 100 N
a) -9 m/s^2 b) -8m/s^2 c)10m/s^2

9. Ex 4- Tension Force problems (continued)
You are on a roof. You decided to lower a can of paint that is attached to a rope. If the can of paint has a mass of 1.5 kg and accelerates downward at 3 m/s2, what is the tension in the rope?

10. Ex 5
A person weighs a fish on a spring scale attached to the ceiling of an elevator as shown in the figure. Show that if the elevator accelerates, the spring scale reads a weight different from the true weight of the fish.