1. Ch 4 Forces in One Dimension
4-1 Force and Motion

2. Force A push or a pull Forces (F) are vectors Magnitude and direction
Despicable Me

3. The Unit of Force a newton (N)
The force required to accelerate a 1 kg mass 1 m/s in 1 second

4. Net Force and Unbalanced Forces
The sum of all forces acting on an object
Unbalanced forces  The net force is not zero
Unbalanced forces cause acceleration
What about constant velocity?

5. System
Object or objects of interest

6. Contact forces A force applied to an object in contact
Objects are touching, in contact

7. Field Forces
Exerted without contact
Gravity
Magnetism

8. Agents The cause of the force
When you push a textbook, your hand (agent) exerts a force on the textbook (system)

9. Free-body diagrams
A physical representation that shows the forces acting on a system
See page 92
Object represented by a dot
Use F for force with subscript
Force vector has proportional length and always points away

10. Net Force The vector sum of all the forces acting on an object
Net Force Causes Acceleration

11. Acceleration and Force
Applying a constant force results in constant acceleration
NOT constant velocity

12. Interpreting Slope Acceleration-Force Graph
What would happen if the force is applied to double the mass?
Results in the following equation

13. Newton’s Second Law of Motion

14. Inertia An object’s resistance to a change in its motion
What happens if the net force acting on an object is zero?
An object’s resistance to a change in its motion
Determined by its mass

15. Newton’s First Law of Motion
Law of Inertia
An object with no net force acting on it remains at rest or moves with constant velocity in a straight line

16. Equilibrium Force The force that produces equilibrium (net force = 0)
Equal in magnitude, opposite in direction

17. 4.2 Weight and Drag force

18. Weight is a Force An apple weighs about 1 newton
The gravitational force on an object
An apple weighs about 1 newton

19. Weight and Mass Weight - The gravitational force on an object
Measured with a ___
Mass - The amount of matter in an object
Measured with a ___

20. Apparent Weight Fscale = ma + mg Fscale = Fnet + Fg (weight) Fnet = ma
What an object appears to weigh on a scale
A measure of the support force
Imagine standing on a scale while being accelerated up or down
Fscale = Fnet + Fg (weight)
Fnet = ma
Fg = mg
Fscale = ma + mg

21. Weightlessness Imagine you are in freefall, what would the scale read?
The support force is zero
Why does an astronaut experience weightlessness
Howard Describes zero gravity

22. Drag Force
The force exerted by a fluid on an object opposing motion through the fluid
Magnitude depends on the velocity and shape or surface area of the object
Also the density and viscosity of the fluid

23. Terminal Velocity The drag force is equal to the force of gravity
So the net force is 0
Acceleration stops

24. 4-3 Newton’s Third Law

25. Interaction Pairs
Two forces acting in opposite directions, have equal magnitude, and act on different objects
Aka action-reaction pair, but is misleading, one doesn’t cause the other

26. Newton’s Third Law of Motion
All forces come in pairs and act on different objects (boy on toy and toy on boy)

27. Tension FT = Fg = mg The force that a string or rope exerts
Force of Tension = force of gravity = weight = mg
FT = Fg = mg
The hanging mass is 1000 grams.
What is the force of tension on the string?

28. Normal Force
The force pushing up on the object, perpendicular to the surface
The book pushes on the table and the table pushes back on the book
Equal to the weight, but opposite in direction

29. FT = Fnet + Fg (weight) Fnet = ma Fg = mg
If the object is moving, what is the force of Tension? An elevator with a mass of 1400 kg accelerates upward at 0.39 m/s/s. What is the force (tension) acting on the support cable?
FT = Fnet + Fg (weight)
Fnet = ma
Fg = mg

30. The larger mass (on the on the frictionless table surface) has a weight of 32 N. The smaller hanging mass has a weight of 26 N.
What is the acceleration of the two boxes?
F = ma
a = F/m
The force is 26 N
The mass is the total mass of the two boxes
What force is exerted on the string?
F = ma
Acceleration is the answer from above
Mass is the mass of the hanging box

32. Net Force Fnet = Fapplied + Ff Ff = Force of Friction (negative)
When sliding or air resistance
Fnet = Fapplied + Ff
Ff = Force of Friction (negative)

33. Net Force Fnet = Fapplied + Fg
When against gravity
Fnet = Fapplied + Fg
Fg = Force of gravity or weight (negative)

35. Mechanics The study of Motion Isaac Newton, 1600’s
The father of mechanics

36. Kinematics
The branch of Mechanics describing motion with out explaining the causes

37. Dynamics
The branch of Mechanics that studies the forces that cause motion

38. The Four Fundamental Forces

39. Gravity An attractive force between all objects
Weakest of the 4 forces

40. Electromagnetic (EM) Force
From the forces between charges
When in motion produce a magnetic force
Holds atoms and molecules together
Photons and light

41. Strong Nuclear Force
Holds the nucleus together against forces of repulsion
Strongest of the four – only acts over a very small distance

42. Weak Nuclear Force
Responsible for radioactive decay (including nuclear fusion in stars)
Linked to the EM force

43. The idea that all forces are aspects of a single force

44. String Theory or Superstring Theory
AKA M-Theory
Particles are replaced by one-dimensional “strings”
The math requires 11 space-time dimensions
Allows for multiverses