Forces

09.18.12

Warm-up

1. What two factors effect the force of gravity?2. How do balanced and unbalanced forces

effect motion?

Forces (pages 21-28)Essential Questions

Finish from other day if you need to.

1. What is a force?2. What is an example of a contact and a

noncontact force?3. What two factors determine the force of

gravity?4. How does friction effect motion?5. How do balanced and unbalanced forces

effect motion?

Forces (pages 21-28)Essential Questions

1. What is a force?push or a pull

2. What is an example of a contact and a noncontact force?contact – frictionnoncontact - gravity

3. What two factors determine the force of gravity?mass and distance

4. How does friction effect motion?works in the opposite direction of motion

5. How do balanced and unbalanced forces effect motion?balanced – stationary or constant speed and directionunbalanced - acceleration

Check for Understanding• Describe how forces apply to the people in these videos.

– Jeb Corliss– Ken Block– Travis Pastrana– Remote Kontrol– Danny MacAskill

• Use four vocabulary terms in your description– Force– Noncontact– Contact– Gravity– Friction– Balanced– Unbalanced

DOL

• A car is traveling at a constant speed and direction.

1. What is a contact force acting on the car?2. What is a noncontact force acting on the car?3. How does friction effect the car?4. Are the forces balanced or unbalanced?

Explain.

Gravity• Depends on mass and distance

Friction

1. Describe 3 areas or instances where having more friction on a bicycle is a “good thing”.

2. Describe 3 areas or instances where having more friction on a bicycle is a “not-so-good thing”?

Other forces

• Magnetic• Aerodynamic drag (fluid friction)• Thrust• Lift• Buoyant

Balanced and unbalanced forces

Notes• Balanced forces

– No motion– Constant speed in same

direction

• Unbalanced forces– Motion– Changing speed or direction

Sim Questions1. What if gravity and

buoyancy are unbalanced?2. What if gravity and

buoyancy are balanced?3. Why does weight change in

water but not mass?

Force diagram vocabulary

• Gravity – always straight down• Normal – opposes gravity, when object is

resting on a solid surface• Buoyant – opposes gravity when object is

suspended in a fluid (liquid or gas)• Applied – “push or pull”• Friction – opposes applied force

Warm-up - CopyForce diagrams

• Gravity – straight down• Normal – opposes

gravity when object is resting on a solid surface

• Applied – push or pull• Friction – opposes

applied force and motion

Aerodynamics of flight

1. What are the four forces impacting flight?2. How is lift generated?3. What is the relationship between weight and

lift?4. What is the relationship between thrust and

drag?

Forces acting on a plane (simplified)

Why reduce aerodynamic drag?

Why increase aerodynamic drag?

Formula 1…Jedi masters of aerodynamics

-List 5 ways the bike reduces aerodynamic drag.

-List 5 ways the rider reduces aerodynamic drag.

Force diagram problems

• A 1000 N couch is being pushed with 450 N of force to right. The friction is 500 N.

• Are the forces balanced or unbalanced?

• Will the couch move?

Applied450 N

Normal1000N

Gravity1000N

Friction500N

Warm-up

• If an object is being pushed with 200 N of force and has 250 N of static friction, will it move? Explain.

Force diagram practice1. A 20,000 N (down) plane has 10,000 N of drag (back) and 50,000

N of thrust (forward) and is able to generate 30,000 N of lift (up). Sketch a force diagram, identify the forces as balanced or unbalanced, and decide if the object is moving.

2. A piece of wood weighing 100 N in placed in a tub of water. The buoyant force on the wood is equal to 100 N. Sketch a force diagram, identify the forces as balanced or unbalanced, and decide if the object is moving.

3. How could one team beat another team in tug-of-war if both teams have the same overall weight and both teams are pulling with the same force? Sketch a force diagram to help explain your answer.

DOL1. Why must engineers consider forces when

designing different modes of transportation? Give specific examples.

2. Force diagramsa) Sketch a force diagram showing an 800 N football

player pushing a 500 N tackling dummy with 1000 N of force. The friction is 250 N.

b) Are the forces balanced or unbalanced?c) Is the tackling dummy moving?