1. Forces

2. Force Forces are measured in Newtons (N)
One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s2.

3. Forces Change Motion Forces usually act in pairs
Forces affect how objects move. They may cause motion; they may also slow, stop, or change the direction of motion of an object that is already moving
Forces act in a particular direction
Forces usually cannot be seen, but their effects can

4. Strength and Direction of Forces
ARROWS
can be used to show forces.
The of an arrow shows the
of the force.
The that the arrow points shows the direction in which the
The stronger the force the the arrow.
LENGTH
STRENGTH
DIRECTION
FORCE WAS APPLIED
LONGER

5. Force: A push or Pull Contact Force Non-Contact Force
A force that can cause or change motion of an object by touching it. Motors and gears operate through contact forces.
Force that results when the two objects are not in physical contact with each other, yet are able to exert a push or pull.
Contact Force Examples:
Friction
Normal Force
Air Resistance
Applied Force
Non-Contact Force Examples:
Gravitational Force
Electrical Force
Magnetic Force

6. Contact Forces
Applied Force: A force typical push or pull, pushing a door open, pulling a rope.
Friction: Happens when two objects rub against each other. Friction opposes motion.
Normal Force: The normal force is the support force exerted upon an object that is in contact with another stable object. For example, if a book is resting upon a surface, then the surface is exerting an upward force upon the book in order to support the weight of the book.
Air Resistance: The air resistance is a type of frictional force that acts upon objects as they travel through the air.

7. Contact Forces
Normal Force= 10N

8. NON-Contact Forces
Magnetic Force: A kind of non contact force, materials such as iron, nickel, cobalt and other magnets just need to be near the magnet to be attracted or repelled.
Electric Force: Noncontact force of electrical charges.
Gravitational Force: The force of attraction between any two objects in the universe. All objects have gravitational force. The mass of an object and its distance determines the strength of its gravitational force.

9. Gravity

10. Forces usually act in pairs

11. Balanced and Unbalanced Forces
Forces occur in pairs and can be either balanced or unbalanced.
Balanced forces do not cause a change in motion. They are equal in size and opposite in direction.
Unbalanced forces always cause a change in motion. They are not equal and opposite.
The final force and its direction are called a resultant, the difference is the net force.
A net force causes an acceleration.
An unbalanced force is needed to change an object’s direction

12. Is There a Net Force?
Combine your prior understanding of acceleration with your newly acquired knowledge that a net force causes an acceleration to determine whether or not a net force exists in the following situations:
YES NO
YES NO
YES
YES

13. Drawing Vectors to Show Force
A force can be shown with a vector. A vector is a line with an arrow. It begins with a dot.
A dot shows where the force begins
The length of the arrow shows the amount of force
The arrows shows the direction
Resultant vectors can be shown as a result of opposite or combined forces

14. Combining Forces - Unbalanced
Forces acting on an object that combine and form a net force that is not zero.
Unbalanced forces cause an object to move.
Forces moving in the same direction are
Forces moving in the opposite direction are
ADDED
SUBTRACTED

15. HMM…. Can you see the unbalanced force here?

16. Combining Forces – Balanced Forces
Forces acting on an object that combine and form a net force of ZERO. NO change in motion.

17. Classify the Forces A foot kicking a soccer ball
An apple falling off a tree
A paper clip sliding towards a magnet
A bat striking a baseball
Two magnets pushing apart from one another
The moon orbiting the Earth
A compass needle turning North
A hand pushing an object
Shoes rubbing against the floor
Have students specify contact or non- contact as well as specific type of force. For example: A foot kicking a soccer ball is a contact force: applied force.