1. Forces and Motion Review Macroscopic Forces
Determine motion from net forces

2. What is a Force? A force is simply a push or a pull.
Forces are Vectors so they have a magnitude and a direction.
A force applied to an object might change its shape (deformation)
A force applied to an object might affect the object’s motion

3. Categories of Forces
Contact forces – requires the objects exerting the forces to touch (be in contact with) each other
Field Forces – act at a distance or through space.
Girl pulls on wagon.
Her weight pushes down on the chair.
Gravitational field
Magnetic field

4. Force Due to Gravity Fg = m g
Gravitational forces occur because the mass of objects causes them pull together.
On Earth, the gravitational force is WEIGHT.
Weight on Earth is calculated by multiplying mass by 9/8 m/s/s (or about 10 m/s/s)
Fg = m g
Direction: always toward the center of the Earth.

5. Friction Force
Frictional forces between two objects depend on the type of surfaces that are in contact with each other
Direction: in the opposite direction of motion or impending motion. Ff

6. Elastic Force
An elastic force applied to an object deforms the object but once removed allows the object to recover its original form, length, shape.
The force present when things stretch or squish
FEL

7. No stretching or squishing
Tension Force
The force that shows up in a string/rope as the result of its stretching is called tension force. Muscles can produce tension forces. FT
No stretching or squishing
Direction: Is always along the ‘rope’

8. Normal or Support Force
Support force between and object and a solid surface
Direction: it is always perpendicular to the surface at the point where the object touches it FN
Direction: 90o to surface

9. Buoyant Force
Force due to a liquid or gas; an object floating in or supported by liquid or air
FBUOY
Direction: Upward

10. Applied Forces FApp FPush FPull
These are forces applied to an object; they can be pushes or pulls; applied forces are not a ‘type’ of force, but a source of a force in a particular problem.
FApp
FPush
FPull

11. Magnetic force FEM FMAG
Magnetic forces are non-contact (or field) forces; a magnetic force can pull an object toward itself or push it away.
FEM
FMAG

12. Common MACROSCOPIC Forces Name: ____________
Symbol
Name of Force
Contact or Field Force?
Direction?
Description
FG or Fg
Gravitational force (or weight force)
Gravitational forces occur because the mass of objects causes them to be attracted to each other. On Earth, the gravitational force is WEIGHT. Weight is calculated by multiplying mass by 9/8 m/s/s (or about 10 m/s/s) Fe
Elastic force
Contact force
An elastic force applied to an object deforms the object but once removed allows the object to recover its original form, length, shape. Ff
Friction force
Frictional forces between two objects depend on the type of surfaces that are in contact with each other; Solid surfaces that are in contact produce friction; Air or liquids can produce frictional forces, too. FT
Tension force
The force that shows up in a string/rope as the result of its stretching ; Muscles can produce tension forces
FN or Fn
Normal force
Support force between and object and a solid surface; it is always perpendicular to the surface at the point where the object touches it
F buoy
Buoyant force
Support force due to liquid or gas ; an object floating in or supported by air or liquid.
F PUSH
F PULL
F APP
Applied force by a person or thing
forces applied to an object; they can be pushes or pulls; applied forces are not a ‘type’ of force, but a source of a force in a particular problem.
F MAG
Magnetic force
Non-contact force (Field force)
a magnetic force can pull an object toward itself or push it away. A magnetic field is present.

13. Common MACROSCOPIC Forces Name: ____________
Symbol
Name of Force
Contact or Field Force?
Direction
Description
FG or Fg
Gravitational force (or weight force)
Non-contact force (Field force)
Toward the center of the Earth
Gravitational forces occur because the mass of objects causes them to be attracted to each other. On Earth, the gravitational force is WEIGHT. Weight is calculated by multiplying mass by 9/8 m/s/s (or about 10 m/s/s)
FEL
Elastic force
Contact force
Varies
An elastic force applied to an object deforms the object but once removed allows the object to recover its original form, length, shape. Ff
Friction force
Opposite direction of motion or impending motion
Frictional forces between two objects depend on the type of surfaces that are in contact with each other; Solid surfaces that are in contact produce friction; Air or liquids can produce frictional forces, too. FT
Tension force
Along the rope, string, etc.
The force that shows up in a string/rope as the result of its stretching ; Muscles can produce tension forces
FN or Fn
Normal force
Always perpendicular (90o) from surface.
Support force between and object and a solid surface; it is always perpendicular to the surface at the point where the object touches it
F buoy
Buoyant force
Upward
Support force due to a liquid or gas ; an object floating in or supported by air or liquid.
F PUSH
F PULL
F APP
Applied force by a person or thing
forces applied to an object; they can be pushes or pulls; applied forces are not a ‘type’ of force, but a source of a force in a particular problem.
F MAG
Magnetic force
a magnetic force can pull an object toward itself or push it away. A magnetic field is present.

15. Vector Addition of Forces

16. +4 N
+3 N =
+7 N
-3 N =
+1 N
+4 N
5 N
3 N =
4 N
Use the Pythagorean Theorem

17. = 0 N 3 N 1 N To the right is positive Up is positive
When the net force is 0 , the forces are BALANCED velocity stays the same.

18. = -1 N 3 N 2 N 1 N To the right is positive Up is positive
When the net force is NOT 0, the forces are UNBALANCED velocity changes SO ACCELERATION OCCURS!!

19. Motion Implications based on Force Analysis
Balanced Forces
Unbalanced Forces
Equal Forces
ΣF = 0
Unequal Forces
ΣF ≠ 0
Static
Equilibrium
Dynamic
Object is at rest. (still)
v = 0 & a = 0
Object is moving at constant velocity.
v ≠ 0 & a = 0
Disequilibrium
Object accelerates in the direction of the net force.
a ≠ 0
Motion Implications

20. A. 60 N ΣF = 6oN + 60 N Net Forces? ΣF = 0 N Equilibrium?
Yes, in the x and y directions.
‘x’ Motion:
At rest or constant vel.
‘y’ Motion:
Net Forces?
Equilibrium?
Motion?

21. B. 12 N 5 N ΣF = 12N + 5 N Net Forces? ΣF = 7 N Equilibrium?
No, in the y direction.
‘y’ Motion:
Accelerates upward
Yes, in the x direction.
‘x’ Motion:
At rest or constant vel.
Net Forces?
Equilibrium?
Motion?

22. C. 6.2 N 2.1 N ΣFy = 6.2N + 6.2 N Net Forces?
ΣFy = 0 N (y direction)
ΣFx = 2.1N
Equilibrium?
Yes, in the y direction
‘y’ Motion:
At rest or constant vel.
No, in the x direction
‘x’ Motion:
Accelerates left
2.1 N
Net Forces?
Equilibrium?
Motion?

23. C. B. A. 12 N 5 N 6.2 N ΣF = 6.2N + 6.2 N ΣF = 0 N (y direction)
Equilibrium?
Yes, in the y direction
‘y’ Motion:
At rest or constant vel.
No, in the x direction
‘x’ Motion:
Accelerates left A.
60 N
ΣF = 6oN N
ΣF = 0 N
Equilibrium?
Yes, in the x and y directions.
‘x’ Motion:
At rest or constant vel.
‘y’ Motion:
2.1 N
ΣF = 12N N
ΣF = 7 N
Equilibrium?
No, in the y direction.
‘y’ Motion:
Accelerates upward
Yes, in the x direction.
‘x’ Motion:
At rest or constant vel.

24. 1. Complete the rectangle
with the vectors
3. To create a balanced force diagram, you need to place a new vector in the opposite direction (but the same magnitude).
2. Draw the diagonal of the rectangle to create the ‘Resultant’ vector..