1. Forces and Newton’s Laws of Motion Newton’s 1st Law
If an object is under the influence of force, does it have to have a displacement? Why or Why not?

2. Forces and Newton’s Laws of Motion
Newton’s First Law

3. Objectives What are Newton’s 1st Law, inertia, and equilibrium?
How are mass and inertia related?
What is net force and how does it determine equilibrium?

4. Newton’s 1st Law of Motion
“An object at rest will stay at rest, and an object in motion will stay in motion with the same speed and direction, unless acted upon by an unbalanced net force.”
Also known as the Law of Inertia
I N E R T I A

5. Inertia
Inertia is the tendency of an object to resist a change in its motion.
Mass is a measure of inertia.
More mass = more inertia
Killer tissue box

6. Newton’s 1st Law of Motion
“An object at rest will stay at rest, and an object in motion will stay in motion with the same speed and direction, unless acted upon by an unbalanced net force.”
What do you think is an “unbalanced net force?”

7. Net Force (∑F)
“the sum of”
The vector sum of all forces acting on an object. “Vector” means direction is important
If the vector sum of the forces is not zero then there is a net force.
∑F ≠ 0, The forces are unbalanced and motion will change. Changing velocity
If the vector sum of the forces is zero then there is no net force.
∑F = 0, The forces are balanced and the motion won’t change. Constant velocity

8. Equilibrium
Balanced forces and a net force of zero describes a state of equilibrium.
Equilibrium: the state in which there is no change in an object’s motion.
The sum of all forces equals zero. FN Fg
ΣFy = FN + Fg = 0
ΣFx =

9. Net Force Balanced on the y-axis Balanced on the y-axis
Balanced on the x-axis
Unbalanced on the x-axis
Equilibrium
Not Equilibrium
Balanced Forces…
No Net Force (∑F = 0)
Constant Velocity
Unbalanced Forces…
Net Force (∑F ≠ 0)
What happens?
*Cart will Accelerate to the right

10. Calculating Net Force Quick Reminder:
An 8 kg monkey is hanging from a vine. What is the tension in the vine?
A 21kg kid is sitting in a swing supported by two cables. What is the tension in each cable?
Two children pull on a stuck toy with a force of 12N at angles of 30º. If the object is in equilibrium (the toy does not move) how much force is resisting the children?
An art piece is hanging in a museum as shown. What is the tension in each chain holding it up if the piece of art has a mass of 20 kg?
Quick Reminder:
Weight is the force on an object due to gravity.
Weight = mass x gravity
Fg = mg
Quick Reminder:
When you see a vector at an angle you break it into it’s components.
12N
30o
Fancy Art
30o

11. S.T.A.M.P.
Curators hang a piece of art from the ceiling in a museum. The cables are at angles as shown. What is the tension in each cable assuming the art has a mass of 500 kg?
67°
180°
Regular
T1= N
T2= 2084 N

12. Practice
A 500 kg container is held in the air by two cables like the picture shown. What is the tension in each cable?
60o
15o
Honors

13. S.T.A.M.P.
A 910 kg car passes through the middle of a bridge. What force must the support beams be able to handle? (Ignore the mass of the bridge)
Honors
55o
30o

14. Exit Ticket
If an object is under the influence of force, does it have to have a displacement? Why or why not?
Has your answer changed since the lesson?