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What Are Forces ?
1. What is a force?
2. How do we measure forces?
3. What are some common examples of forces
Questions
http://nnhsphysics670.pbworks.com/Intro-Forces-and-Free-Body-Diagrams
1. What is a Force?Definition
Term Term Symbol Unit Unit Symbol
1. What is a Force?Definition
Term Term Symbol Unit Unit Symbol
force F newton N
A force is a push or a pull. A force is a push or a pull.
What would you do to get a box to start moving?
What would you do to get a box to start moving?
Everyday language
Physics language
What would you do to get a box to start moving?
Everyday language
Physics language
To get the box to start moving I would PUSH the box.
To get the box to start moving I would PUSH the box.
What would you do to get a box to start moving?
What would you do to get a box to start moving?
Everyday language
Physics language
To get the box to start moving I would PUSH the box.
To get the box to start moving I would PUSH the box.
What would you do to get a box to start moving?
Everyday language
Physics language
To get the box to start moving I would PUSH the box.
To get the box to start moving I would PUSH the box.
To get the box to start moving I would APPLY a FORCE.
To get the box to start moving I would APPLY a FORCE.
Consider Tug-of-War
Consider Tug-of-War
Sarah’s team applies a ____________of 10 _______ to the ___________ on the rope.
10 N
Consider Tug-of-War
Sarah’s team applies a___FORCE___of 10 NEWTONS to the ___LEFT________ on the rope.
10 N
Consider Tug-of-War
Jaya’s team applies of ____________of 10 _______ to the ___________ on the rope.
Consider Tug-of-War
Jaya’s team applies of ___FORCE___of 10 NEWTONS to the ___RIGHT________ on the rope.
10 N
Balanced Forces
The __________ are ______________ in magnitudebut ___________________ in direction.
10 N10 N
Balanced Forces
The FORCES are EQUAL in magnitudebut OPPOSITE in direction.
10 N10 N
Unbalanced Forces
20 N10 N
Unbalanced Forces
20 N10 N
10 N
The ____________is 10 newtons.
Unbalanced Forces
20 N10 N
10 N
The _NET FORCE__ is 10 newtons.
Net Force
If two forces are acting in the same direction, they add together.
…the impact of all forces acting on an object…
Net Force
Example: Imagine Cindy is pulling a wagon to the right with a force of 5N, and Kelly is pushing the wagon to the right with a force of 7 N:
1. Draw an arrows to represent these forces on the wagon below.
2. What is the net force on the wagon? _____N + ____ N = _____ N3. In what direction does the force act? _____________________4. The forces are _______________.
Net Force
If two forces are acting in opposite directions, they subtract.
…the impact of all forces acting on an object…
Net Force
Example: Imagine Peter is pulling a treasure chest to the left with a force of 10 N, and Brian is pulling the treasure chest to the right with a force of 7 N.
1. Draw an arrows to represent these forces on the wagon below.
2. What is the net force on the wagon? _____N - ____ N = _____ N3. In what direction does the force act? _____________________4. The forces are _______________.
Balanced Forces(net force = 0)
Unbalanced Forces(net force ≠ 0)
No change in motion
Change in motion
Balanced vs. Unbalanced Forces
Let’s look at two scenarios:
1. You are sitting on a chair. Do you think the forces on you are balanced? Why or why not?
Balanced vs. Unbalanced Forces continued…
2. A space shuttle is taking off. Do you think the force is balanced or unbalanced? Why or why not?
Question: How do unbalanced forces change motion?
1. ______ things up
2. ______ things down
3. Make things ______.
Practice with Net Force
magnitude how much?
units newtons
direction right, left, up, down
For you to Try:
• Worksheet--Practice with Net Force
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