FORCES AND
THE LAWS OF MOTION
CHAPTER 4
CHAPTER4
• Section 1: Changes in Motion
• Section 2: Newton’s First Law
• Section 3: Newton’s Second and Third Law
• Section4: Everyday Forces
FRIDAY JANUARY 8TH
Describe how force affects the motion of an object.
Interpret and construct free body diagrams.
FORCES
FORCE
• A force is an action exerted on an object which may change the
object’s state of rest or motion.
In other words….
• Forces can cause accelerations.
Change the velocity of an object…
Acceleration = change in velocity
change in time
• The SI unit of force is the newton, N.
• Forces can act through contact or at a distance.
CONTACT VS FIELD FORCES
• Contact forces: result from physical contact between two
objects (applied force, normal force….)
• Field Forces: do not involve physical contact (gravity,
electrostatic repulsion/attraction)
FORCE DIAGRAMS
• The effect of a force depends on both magnitude and
direction. Thus, force is a vector quantity.
• Diagrams that show force vectors as arrows are called force
diagrams.
• Force diagrams that show only the forces acting on a single
object are called free-body diagrams.
Chapter 4
Section 1 Changes in Motion
FORCE DIAGRAMS, CONTINUED
Force Diagram
Free-Body Diagram
In a force diagram, vector
arrows represent all the
forces acting in a situation.
A free-body diagram shows
only the forces acting on
the object of interest—in
this case, the car.
PRACTICE
• Draw a free-body diagram of the toy these
puppies are playing with.
HOMEWORK
• Copy the example on page 121. (copy all the bold text into
your notes.)
• Complete practice questions 1-2 on page 122
• And section 1 formative assessment questions 2, 3, 4, 5