Newton’s Laws Forces in Motion!

Forces A force is a push or a pull.

If the forces are balanced (same), there is no movement In a tug of war contest, the forces are balanced when neither side is “winning.”

If the forces are unbalanced, there is movement! In a tug of war contest, the forces are unbalanced when a side is “winning.” The greater force will always result in movement in its direction!

Tug of War Video Clips http://www.streetfire.net/video/dodge-vs-chevy-diesel-truck-tug-of-war_163521.htm http://www.youtube.com/watch?v=H631yvjC6j8&feature=related

If the forces are the same (balanced), there is no movement The force you exert pushing down on a chair must equal the force of the chair pushing up. Otherwise, if your push was more, the chair would fall apart. If the chair’s push was more, you’d be ejected!

If the forces are unbalanced, there is movement! The greater force will always result in movement in its direction!

Newton’s First Law of Motion aka Law of Inertia An object at rest remains at rest and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalance force.

Object at rest = not moving = balanced forces

Objects in motion = unbalanced force = move forever at the same speed and direction until something makes it Stop! What can stop it? Gravity, friction and other objects!

Inertia the tendency of all objects to resist any change in motion. If it is still, it WANTS to stay still! If it is moving, it WANTS to stay moving! http://video.search.yahoo.com/search/video;_ylt=A0oG7kW8RRtNFT4AJgxXNyoA?ei=UTF-8&p=inertia&fr2=tab-web&fr=yfp-t-311

Inertia is effected by… The amount of mass more mass = more inertia less mass = less inertia Something with greater mass is hard to start moving and harder to stop.

Newton’s First Law of Motion is called The unbalanced force law The balanced force law The law of Inertia The law of movement

Inertia is 1) related to mass 2) related to gravity 3) the tendency of something not to want to change its movement 4) 1 and 3

Newton’s Second Law of Motion the acceleration of an object depends on the mass of the object and the amount of force applied. #1) The ability to change the speed of an object depends on the mass of the object. More mass = harder (think inertia)

The ability to change the speed of an object depends on the force The ability to change the speed of an object depends on the force. More force = increases acceleration Less force = decreases acceleration (Duh! Push something hard, it moves FASTER) http://dsc.discovery.com/videos/time-warp-sumo-wrestling.html

(1 = yes or 2 =no) To increase acceleration you can Increase mass Increase force Decrease mass Decrease force

If you increase force, what will happen Acceleration will decrease Acceleration will increase Mass will decrease Mass will increase

If you increase mass and want to keep the same acceleration, you must Decrease force Increase force Increase inertia Decrease inertia

Newton’s Third Law Whenever one objects exerts a force on a second object, the second object exerts an equal and opposite force on the first. Also known as, for every action, there is an equal and opposite reaction!

All forces work in pairs.

Two forces always act at the same time Action force – the first one. Reaction – the opposite one. The force of the rockets push down (action force) so the space shuttle moves up (reaction force)

Force pairs NEVER act on the same object Swimming – Hands (action force) pushes through water. Water (reaction force) pulls the body through the water Jumping – Legs (action force) push against the ground Ground (reaction force) pushes against you

Review 1. Give an example of Newton’s 1st law. 2. Give an example of Newton’s 2nd law. 3. Give an example of Newton’s 3rd law.