Physics Day 42 – FBD

-LO: FBD with numbers

-LO: FBD for Static problems

AGENDA

Do Now

Finish WS1

Notes

Do Now – 1. Please draw a Free Body Diagram of a 5kg book lying on a table being pulled by a string to the right with a force of 3N. (not moving)

What is force do?

• How do we change motion in velocity or only direction? Why some objects accelerate at higher rates than others do?

• A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects.

• Forces cause changes in velocity over time, or accelerations.

Type of forces

• Contact Forces

• Frictional Force

• Tension Force

• Normal Force

• Air Resistance Force

• Applied Force

• Spring Force

Type of forces

• Action-at-a-Distance Forces

• Gravitational Force

• Electrical Force

• Magnetic Force

Normal Forces

Physics Book

Table

Normal Forces

Physics Book

Table

a = 0

FgFn

Friction

Physics Book

Table

a = 0, v = 0

FgFn

The force of friction is zero because the book is not trying to slide in any direction. If you put a friction force in, it would be unbalanced and cause an acceleration (and that never happens)

Friction

Physics Book

Table

String tied to book

Friction

Physics Book

Table

a = 0 (constant velocity to the right)

Fg

Fn

Fstring

String tied to book

Fµ

Equilibrium and Statics

When all the forces that act upon an object are balanced, then the object is said to be in a state of equilibrium.

The forces are considered to be balanced if the rightward forces are balanced by the leftward forces and the upward forces are balanced by the downward forces.

Determining the Net Force

• An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Spring Forces

• Stretched spring Fs< 0

• Equilibrium Fs=0

4.00 kg

The object hung from the cable has a weight of 25 N. Write the equation for the sum of the forces in the y-direction. What is the tension in the cable? Repeat the problem above with a 5 degree angle. How does the tension compare?

The object hung from the cable has a weight of 25 N. Write the equation for the sum of the forces in the y-direction. What is the tension in the cable? Repeat the problem above with a 5 degree angle. How does the tension compare?

2TSin30 = 25NT=25N

T2Cos30 = 30NT2Sin30 = T1

T2 = 2*T1

T2 = 30N/0.87T2 = 34.5NT1 = 69N

Use g = 10 m/s/s

W=mg = 20 kg * 10 m/s/s = 200N

Fn = mgCos30 = 200N*cos30 = 174N

How did we do that?