1. Bell Ringer Socrative Quiz- Newton’s Laws Room: LEE346
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2. Objectives We will analyze the forces acting on an object.
I will draw free body diagrams and analyze the force, mass and acceleration of an object using Newton’s 2nd law, F=ma

3. Forces SI Unit for Force is the Newton (N)
The formula for force is F = ma
NOTE: the unit for mass is kg and the unit for acceleration is m/s2… so a kg•m/s2 is the same thing as a Newton!

4. Forces
A force causes an object to change its velocity, by a change in speed OR direction
Force is a vector quantity since direction is important
Vectors in Opposite directions– SUBTRACT
Vectors in same directions- ADD

5. Free-body diagrams
A free body diagram shows the magnitude and direction of all forces acting on a single body, usually drawn as a box with arrows.
The diagram shows the body only and the forces acting on it.

6. Forces and Free Body Diagrams (FBD)

7. Type of Force
Symbol
Description
Frictional
Ffrict
force exerted between surfaces as an object moves across it
Tension
Ftens
force transmitted through a string, rope, cable, or wire
Normal
Fnorm
force exerted on an object when it is on top of another object; ┴ to resting plane
Air Resistance
Fair
force exerted on object as it travels through the air; usually negligible
Applied
Fapp
force on an object being pushed or pulled
Spring
Fspring
force exerted by a stretched or compressed spring with an object attached to it
Gravitational
Fgrav
force of gravity that all objects on Earth experience

8. Free Body Diagrams (FBD)
Directions for drawing FBDs :
1. Draw the object as a box
2. The larger the force the longer the vector arrow should be
3. The direction of the in the direction that the force is acting
4. Always label your force vectors
5. With balanced forces/ constant velocity vectors are equal
6. With unbalanced forces/ acceleration/deceleration vectors are unequal

9. FBD Example
A book on a table is being pushed to the right at a constant velocity

10. FBD Example
A parachutist jumps out of an airplane; include air resistance

11. How would I draw the FBD?

12. How would I draw the FBD?
This is what the FBD should look like!

13. How would I draw the FBD?

14. How would I draw the FBD?

15. How would I draw the FBD?

16. Examples
Mass hanging on a rope
T (tension in rope)
W (weight)

17. Examples Inclined slope
Force of Gravity is always straight down. The Normal force is perpendicular (90° ) to surface.
Inclined slope
FN (normal force)
Ff (friction)
Fg(weight)

18. Pulled / Pushed at an angle

19. Solving

20. Net force
Net Force- sum of the forces acting on object in a given direction.
(horizontal & vertical separately)

21. Net Force ? ? ?

22. Net Force

23. It’s physics, there’s always a mathematical relationship!
Newton’s 2nd law
There is a mathematical relationship between the net force and acceleration.
net force (N) = mass (kg) x acceleration (m/s2)
It’s physics, there’s always a mathematical relationship!
Fnet = ma

24. Example What will be Mr. Porter’s acceleration?
Mass of Mr Porter and bike = 100 kg
Pushing force (100 N)
Friction (60 N)

25. An example net force = 100 – 60 = 40 N moving to the left FNet = ma
a = 0.4 m/s2
Mass of Mr. Porter and bike = 100 kg
Applied force (100 N)
Friction (60 N)

26. Remember Weight = Fgrav = mX a Fgrav= m X g Use g as 9.8~ 10 m/s2
Also Remember, Fnorm = Fgrav