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Force - a push or pull on an object

 A force can change the

direction

of an object.

 Scientists express force using a unit called the

Newton

(N). One Newton of force is the amount needed to accelerate a mass 1kg in size

1.0 m/s/s

.



Forces

affect how objects move.

Motion

is any physical movement or change in

position

or place.

 The starting point you use to describe the motion of an object is called the

reference point

.

 While using a reference point to describe motion, you will also need to state the

direction

of the movement.

 Direction may be up or down, right or left, north or south, east or west, etc.

PRACTICE

 Describe the force needed to put each object in motion.

Net Force is the combination of ALL the forces acting on an object. The Net Force is dependent upon the direction of the forces.

 Balanced Forces =

NO

Motion  The net force = Zero  Unbalanced Forces =

MOTION

 The net force = SUM of the two forces

 When two unequal forces act in

opposite

directions on an object, the net force is the

difference

of the two forces. The final force and its direction are called a resultant.

      1. The forces shown above are PUSHING / PULLING forces.

2. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.

3. The forces are EQUAL / NOT EQUAL.

4. The forces DO / DO NOT balance each other.

5. The resultant force is 1000 N TO THE RIGHT / 1000 N TO THE LEFT / ZERO.

6. There IS / IS NO motion.

Answers:

1. The forces shown above are PUSHING /

PULLING

forces.

2. The forces shown above are WORKING

TOGETHER /

OPPOSITE FORCES.

3. The forces are

EQUAL

/ NOT EQUAL.

4. The forces

DO

/ DO NOT balance each other.

5. The resultant force is 1000 N TO THE RIGHT /

1000 N TO THE LEFT / ZERO

.

6. There IS /

IS NO

motion.

      1. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES. 2. The forces are EQUAL / NOT EQUAL.

3. The forces DO / DO NOT balance each other.

4. The stronger force is pulling to the RIGHT / LEFT.

5. The weaker force is pulling to the RIGHT / LEFT.

6. Motion is to the RIGHT / LEFT.

Answers:

1. The forces shown above are WORKING

TOGETHER /

OPPOSITE FORCES.

2. The forces are EQUAL /

NOT EQUAL.

3. The forces DO /

DO NOT

balance each other.

4. The stronger force is pulling to the RIGHT / LEFT.

5. The weaker force is pulling to the LEFT.

RIGHT /

6. Motion is to the RIGHT / LEFT.

Forces Acting on Objects

 Depending on the situation, there will be certain forces acting upon an object.

 Here are a few forces that we will be using for this unit: 

Normal

Force: The support force applied to an object that is in contact with another stable object.



Gravity

Force: The force with which the earth, moon, or other massively large object attracts another object towards itself. Gravity will always be a force acting on an object.



Air Resistance

: A special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to

oppose

the motion of an object.

Vectors

 Despicable Me Clip: DIMbI8  A

vector

shows the

direction

and the magnitude (amount) of a force.

 It is a line with an arrow and begins with a dot.

 The length of the arrow shows the amount of force.

 The arrow shows the direction of the force.

Force Diagrams

 A science book is at rest on a table top. Diagram the forces acting on the science book.

 A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting on the skydiver.  Two teams are competing in a tug-of-war contest. Team A is pulling at 4000N and Team B is pulling at 4900N is the opposite direction. Sketch the forces and show the net force exerted. Which team is winning? Is this force balanced or unbalanced?  Tommy and John are trying to move a large table. John pushes with a force of 1150N and Tommy helps him by pushing on the same side of the table with a force of 800N. Sketch the individual forces exerted on the table and then calculate and show the net force exerted on the table.

A science book is at rest on a table top. Diagram the forces acting on the science book.

A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting on the skydiver.

Two teams are competing in a tug of-war contest. Team A is pulling at 4000N and Team B is pulling at 4900N is the opposite direction. Sketch the forces and show the net force exerted. Which team is winning? Is this force balanced or unbalanced?

Tommy and John are trying to move a large table. John pushes with a force of 1150N and Tommy helps him by pushing on the same side of the table with a force of 800N. Sketch the individual forces exerted on the table and then calculate and show the net force exerted on the table.

Calculating Net Force Examples

 An object has 2 forces pushing on the left. One force is 30 N and the other force is 15 N. What is the net force? Is it balanced or unbalanced? What direction is the object moving?  An object has a force of 10 N pushing from the left and 2 forces (15 N and 5 N) pushing from the right. What is the net force? Is it balanced or unbalanced? What direction is the object moving?

What do you think the activity in the beginning of class was demonstrating?