1. Forces to recon with!

2. Contact Force is a force that acts at the point of contact between two objects
Non-contact forces do not require contact
Contact Forces
Magnetic:
Static:
Gravity:

3. An attractive force that exists between all objects that have mass.
This force is dependent on mass and distance from the object.
Gravity

4. Weight vs. Mass Mass: Amount of matter in an object.
What is the difference?
Weight: Is the gravitational force exerted on an object.
Your weight is actually a force measured in Newton’s.
Weight vs.
Mass

5. Gravity and Air Resistance
Most objects falling through air experience a type of fluid friction called air resistance.
The greater the surface area of the object the greater the air resistance. (paper drop)
However, since the elephant has more mass, it has more downward force of gravity and falls faster.
Gravity and Air Resistance

6. An object is in free fall when the only force acting on the object is gravity.
Free-falling objects do not encounter air resistance.
In free fall, the force of gravity is an unbalanced force.
Gravity and Free Fall
Take away ALL air, so that only the force of
Gravity is being used.

7. All objects in free fall accelerate at the same rate – 9
All objects in free fall accelerate at the same rate – 9.8 m/s² - regardless of their mass.
in one second = 9.8 m/s²
in two seconds = 19.6 m/s²
in three seconds = 29.4 m/s²
in four seconds = 39.2 m/s²
The velocity continues to increase as the object falls.
Calculating Free Fall

8. Universal Gravitation
The law of universal gravitation states that the force of gravity acts between all objects in the universe.
Universal Gravitation

9. Friction is a force that resists the motion of two surfaces that are touching.
When a moving object comes in contact with another object, friction is the opposing force that slows or stops the moving object.
What is Friction?
Static friction prevents objects from sliding
Sliding friction resists objects while they are moving
Fluid friciton involves air or water

10. Sliding Friction
A resistance to movement that is created when two things rub together.

11. Ways to Reduce Friction
Smooth the surface
Put ball bearings in wheels
Replace rolling with sliding
Add oil or another type of lubricant
Ways to Reduce Friction

12. A World Without Friction
Without friction, an object would continue to move at constant speed forever.
The strength of the force of friction depends on the type of surfaces and how hard the surfaces push together.
Rough surfaces produce greater friction than smooth surfaces.

13. The force that tries to slow objects down when they move through a liquid or a gas. It's also known as "drag", or "air resistance".
All gases and liquids are fluids.
An airplane and a swimmer both experience fluid friction.
Fluid Friction