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# Force - PowerPoint PPT Presentation

Force. Definition: A push or a pull Force can cause motion SI unit -> Newton (N)= 1 kg x 1 m/s 2 Sometimes pound ( lb ) can be used as a unit for force 1 Newton=0.22481 pounds force. Combining Forces. Balanced Force Equal and opposite forces = ‘balanced’

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## PowerPoint Slideshow about ' Force' - duane

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Presentation Transcript

Definition:

• A push or a pull

• Force can cause motion

• SI unit -> Newton (N)= 1 kg x 1 m/s2

• Sometimes pound (lb) can be used as a unit for force

• 1 Newton=0.22481 pounds force

• Balanced Force

• Equal and opposite forces = ‘balanced’

• Balanced forces give no motion

No motion of hands

• Unbalanced force – more force in one direction (net force)

• Bigger force to the right

• Smaller force to the left

• Net force to the right

• Friction – a force that opposes motion

• Caused by the interaction between two touching surfaces rubbing against each other

• Four Types

• Friction that acts on something that is not moving

• No heat or wear is generated

• Force resulting when pushing or pulling an object over a surface.

• Contact is reduced because of rollers or wheels or ball bearings.

• Resistance from a “fluid”

• Fluids are liquids and gases.

• A smooth surface does not demonstrate as much friction as a rough surface.

• Waxing, oiling, etc. can be used to reduce friction.

• µ= “coefficient of friction”  represents the roughness of the surfaces in contact.

• In reality there two main subtypes:

• µs- Static friction to get it moving

• µk- Kinetic friction to keep it moving

• µs> µk needed for movement to occur

• Gravity

– force of attraction between two objects

---> pulling force

Factors Affecting Gravity

• Mass – more mass, more gravity

• Distance – closer, more gravity

http://www.exploratorium.edu/ronh/weight/

• 1. Describe three ways in which a car’s velocity will change

• 2. Identify a one situation involving unbalanced force and one situation involving balanced force. Explain how it each affect the motion of an object.

• 3. Arrange the following pairs of surfaces in order of most friction to least friction

• A shoe sole and a waxed basketball court

• A shoe sole and the frozen surface of a lake

• A shoe sole and the sidewalk

• 4. Explain why Venus, which is slightly less massive than Earth, experiences a stronger gravitational pull from the sun than Earth does.

• 5. What is the average acceleration of a scooter that starts at rest and moves straight ahead at 12 m/s in 24 s.

• 6. Which will be moving faster after 3.0 s, a cyclist maintaining a constant velocity of 15 m/s straight ahead or a race car accelerating forward from a stoplight at 4.0 m/s2?