Download 12-2 Notes: What Is a Force?

12-2 Notes: What Is a Force?
A force is a push or pull. All forces have two properties: direction and magnitude.
A newton (N) is the unit used to describe the magnitude, or size, of a force.
A force can change the velocity of an object. This change in velocity can be a
change in speed, direction, or both. In other words, forces can cause acceleration.
Anytime you see a change in an object’s motion, you can be sure it was caused by
a force. However, a force can act on an object without causing the object to move.
The net force is the combination of the forces acting on an object. When two forces
act in the same direction on an object, the two forces can be added to find the net
force. The length of the arrows represent the magnitude of the forces. The longer
the arrow, the larger the force.
When forces act on an object in opposite directions, the net force is found by
subtracting the smaller force from the larger one. The net force is in the same
direction as the larger force.
When the forces on an object produce a net force of 0 N, the forces are balanced.
Balanced forces will not cause a change in the motion of an object. Many objects
that have balanced forces acting on them are not moving, or are static. Tension is a
force that is exerted when matter is pulled or stretched. Compression is a force that
is exerted when matter is pushed or squeezed.
When the net force on an object is not 0 N, the forces on the object are unbalanced.
Unbalanced forces cause a change in the velocity of objects. The change in
velocity may be a change in speed, a change in direction, or both. Unbalanced
forces will also cause a static object to start moving or cause a moving object to
slow down or stop moving.
Every moving object started moving because an unbalanced force acted on it, but it
can keep moving without an unbalanced force acting on it. Unbalanced forces can
cause a change in the direction of motion. However, objects do not always move in
the direction of the unbalanced force.
Unit 5 (Ch. 12) – Motion & Forces
Bach
01/06/10
Section 12-2 Review
1. What two properties do all forces have?
Forces have direction and magnitude.
2. What are three different ways in which a force can change the
velocity of an object?
By causing it to increase in speed, decrease in speed, or change
direction.
3. What is net force?
Net force is the combination of all the forces acting on an object.
4. How do you calculate the net force on an object when two or
more forces act in the same direction?
You add the forces to find the net force of two or more forces acting
in the same direction.
5. What is the net force on an object if a force of 7 N north and a
force of 5 N south act on the object?
2 N north
6. How do you know that the forces on a hanging light are
balanced? What forces act on the light?
I know that the forces acting on a hanging light are balanced because
the light does not move. The forces on the light arte the force of
gravity pulling downward and the force of tension in the cable pulling
upward.
7. What can happen to the velocity of an object when unbalanced
forces act on it?
When unbalanced forces act on an object, the velocity of the object
changes (it accelerates). The change can be an increase or decrease
in speed, a change in direction, or both.
8. Are the forces on a kicked soccer ball balanced or unbalanced?
How do you know?
Unbalanced, because the ball changes speed and/or direction.
Unit 5 (Ch. 12) – Motion & Forces
Bach
01/06/10
12-2 Notes: What Is a Force?
A ________ is a push or pull. All forces have two properties: direction and
_____________. A __________ (N) is the unit used to describe the magnitude, or
size, of a force.
A force can change the __________ of an object. This change in velocity can be a
change in speed, ____________, or both. In other words, forces can cause
________________. Anytime you see a change in an object’s motion, you can be
sure it was caused by a _________. However, a _________ can act on an object
without causing the object to move.
The _____ _________ is the combination of the forces acting on an object. When
two forces act in the same direction on an object, the two forces can be _________
to find the net force. The __________ of the arrows represent the magnitude of the
forces. The longer the arrow, the __________ the force.
When forces act on an object in opposite directions, the net force is found by
______________ the smaller force from the larger one. The net force is in the
same ____________ as the larger force.
When the forces on an object produce a net force of 0 N, the forces are
___________. Balanced forces will not cause a __________ in the motion of an
object. Many objects that have balanced forces acting on them are not moving, or
are ________. __________ is a force that is exerted when matter is pulled or
stretched. ________________ is a force that is exerted when matter is pushed or
squeezed.
When the net force on an object is not 0 N, the forces on the object are
________________. Unbalanced forces cause a change in the ___________ of
objects. The change in velocity may be a change in _________, a change in
direction, or both. Unbalanced forces will also cause a _________ object to start
moving or cause a ____________ object to slow down or stop moving.
Every moving object started moving because an _______________ force acted on
it, but it can keep ___________ without an unbalanced force acting on it.
Unbalanced forces can cause a change in the _____________ of motion. However,
objects do not always move in the direction of the ________________ force.
Unit 5 (Ch. 12) – Motion & Forces
Bach
01/06/10
Section 12-2 Review
1. What two properties do all forces have?
2. What are three different ways in which a force can change the
velocity of an object?
3. What is net force?
4. How do you calculate the net force on an object when two or
more force act in the same direction?
5. What is the net force on an object if a force of 7 N north and a
force of 5 N south act on the object?
6. How do you know that the forces on a hanging light are
balanced? What forces act on the light?
7. What can happen to the velocity of an object when unbalanced
forces act on it?
8. Are the forces on a kicked soccer ball balanced or unbalanced?
How do you know?
Unit 5 (Ch. 12) – Motion & Forces
Bach
01/06/10