1. Forces and Newton’s Laws of Motion
1. “What is a force?”
2. “Do objects need to touch to experience a force?”
DSQ
What is a force?
Do objects need to touch to experience a force?

2. Forces and Newton’s Laws of Motion
Forces and Diagrams

3. What We Want to Know
What is force, and what types of forces are there?
What is the difference between mass and weight?
What are the advantages of drawing free-body diagrams when analyzing forces?

4. A Little History… Aristotle a famous Greek philosopher around 400 BC
Natural Motion…
objects seek their natural resting places
Not caused by force
Violent Motion…
Result of forces that push or pull an object
External cause… moving against nature
No force… No motion
Do you agree?

5. A Little History…
Galileo the foremost scientist of the late-Renaissance
Asked how things moved rather than why
Demolished the notion that force is necessary to keep an object moving
Only when friction is present is force required to keep objects moving
Without frictional force, an object’s motion will continue
Open the door for Isaac Newton and his Laws of Motion

6. Describe the ball The ball’s motion will not change on its own.
Something must cause an objects motion to change.

7. Force
Force: a push or pull on an object which may change an objects state of rest or motion.
Forces cause a change in an object’s speed and/or direction.
Forces cause acceleration.
Forces are measured in Newtons (N).
Forces only exist as a result of objects interacting.
If their interaction stops, then there is no force.

8. Force
The forces that result from the interactions can be generalized as either contact forces or field forces.

9. Contact Forces
Contact Forces: forces resulting from actual physical contact between objects.

10. Field Forces
Field Forces: forces that are exerted from an interaction between objects, despite not being in physical contact with one another.

11. Examples Contact Forces Field Forces Applied Forces Tension Forces
Spring Forces
Frictional Forces
Normal Force
Field Forces
Gravitational Forces
Magnetic Forces
Electrical Forces

12. Weight vs. Mass Weight is the force of gravity acting on an object.
The value of weight varies depending on where you are. ie. Earth, the Moon, another planet, etc.
Weight = mass x gravity (W = mg)
Mass is the amount of matter in an object.
The value of an objects mass is the same everywhere and does not change on location.

13. Normal Force Normal Force: Results from contact with a surface.
The force that acts perpendicular to the surface.

14. Vectors Forces are vectors
Force (F) q
Forces are vectors
Have a magnitude and direction.
Can be added or subtracted to form a resultant.
Can be resolved into components.
Force and free-body diagrams can help analyze forces at work.
Vertical
Component
Horizontal

15. Force and Free-body Diagrams
Force diagrams: shows all interacting objects and forces.
Free-body diagrams: help analyze situations by isolating a single object and the forces that are acting on that object.

16. Example Diagram

17. Practice Draw a free-body diagram for: A book sitting on a table.
A person starts a cart rolling down a ramp.
The cart rolling down a ramp.
A box at rest on a ramp.
A person pulling a sled across a frozen lake.
A bus being pushed over rocky terrain.

18. Objectives What is force, and what types of forces are there?
What is the difference between mass and weight?
What are the advantages of drawing free-body diagrams when analyzing forces?

19. Exit Ticket
Reflect on your answers to “What is a force?” and “Do objects need to touch to experience a force?”
Are your answers different now than they were before?
Why did you think that way?