Download 4.1 Changes in motion

Chapter 4: Forces and the Laws of Motion

Forces cause changes in velocity
 We usually imagine a force as a push or a pull on
an object.
 Force – the cause of an acceleration, or the
change in an object’s velocity.
▪ What are three ways to change a velocity?

The units for force
Important equivalents: 1 N = 0.225 lb

Forces can act through contact or at a
distance.
 Contact force – force that arises from the physical
contact of two objects.
▪ What are some examples?
 Field force – force that can exist between objects,
even in the absence of physical contact between
the objects.
▪ Gravitational field force between any two masses
▪ Electrical field force between any two charges particles.
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
Force is a vector
 The effect of a force on an object depends on the
magnitude and direction of the force.
 Force diagram – a diagram of the objects
involved in a situation as well as the forces acting
on the objects.

A free-body diagram helps analyze a
situation.
 Shows only the object of interest and the forces
acting on it.
 A free-body diagram in practice:
▪ Draw a simple shape to represent the object
▪ Then draw all the identified forces coming out of the
object, each indicating both magnitude and direction.