Newton’s Laws

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# Newton’s Laws - PowerPoint PPT Presentation

Newton’s Laws. Force. Force  a push or a pull Causes object to start or stop moving or change direction. force of table. g. Combining forces. Two men paddle their canoe on a river. force of paddling. force of current. combined forces. force of paddling. force of current.

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### Newton’s Laws

Force
• Force a push or a pull
• Causes object to start or stop moving or change direction

force of table

g

Combining forces
• Two men paddle their canoe on a river

force of current

combined forces

force of current

combined forces

force of current

combined forces

Opposition to Motion
• Friction a force that opposes motion
• Caused by rough surfaces of all materials

razor\'s edge

3 Types of Friction

1. Sliding when solid objects grind over each other

• puck and ice

2. Rolling wheels spinning on an axle

• skateboards eventually roll to a stop

3. Fluid liquids or gases slow the motion of a solid

• wind resistance
• oil a squeaky hinge
• pushes a surfer
• http://www.sciencejoywagon.com/physicszone/lesson/01motion/projecti/airproj/default.htm
Newton’s 1st Law
• Greeks thought that the natural state of an object was at rest.
• ex. A ball stops rolling
• without friction an object would never stop!
• Newton’s 1st an object in motion tends to stay in motion; an object at rest tends to stay at rest
Newton’s 1st Law
• Inertia property of matter that resists a change in motion
• An object with great mass has high inertia
Newton’s 2nd Law

f = m x a

A

FA = 1000 kg x 0.05 m/s/s

FA =

50N

B

FB = 2000 kg x 0.05 m/s/s

FB =

100N

Newton’s 2nd Law
• Force = mass x acceleration
• An object will only accelerate if there is an unbalanced force
Newton’s 3rd Law
• For every action there is and equal and opposite reaction
Newton’s 3rd Law
• For every action there is and equal and opposite reaction
• A bird pushes down on the air and the air pushes up on the bird
Gravity

force of hand

g

With the upward force of the floor equilibrium is attained and there is no motion

Without the upward force of the hand there is not equilibrium of forces and motion occurs

Gravity: air resistance
• Opposes downward motion of falling objects.
• Larger surface areas increases air resistance
Gravity: universal gravitation
• All objects in the universe are attracted to each other through gravity
• More mass in an object more gravity
Newton’s Laws
• 1st Law: (inertia: objects tend to do what they are doing)
• cannon ball will rest until a force is put on it
• ball will roll straight until ramp puts a force on it
• 2nd Law: (f = m x a)
• greater force put on ball accelerates it more
• greater mass of ball but greater force on water
• 3rd Law: (every action has an equal but opposite reaction)
• ball moves right, cannon recoils left
• ball move down, water splashes up
Potential Energy
Gravity: terminal velocity
• The fastest a falling object can fall due to air resistance
• An object will not accelerate if the forces are equal.
• When the force of gravity is equal to air resistance the skydiver will not accelerate.
• When the skydiver’s air resistance is greater than the force of gravity the skydiver will slow down.
Newton’s 1st Law

Experiment 1: Place the card on top of the cup. Take one coin and place it on the center of the card. Without lifting the card, try to get the coin into the cup. What is the best procedure?

Experiment 2: Stack several coins (4 or more) on a smooth table top. Place one coin a short distance from this stack. Flick the coin very quickly at the stack. What happens? Vary the speed of your flicking and observe the results.

Paper & Beaker Egg & Sheet

Newton’s 3rd Law
• A mouse trap is attached to a cart. The trap is set with a piece of string and a bag of lead shot is placed on the trap. When the string is cut or burned trap throws the bag of shot in one direction which causes the cart to take off in the opposite direction.

balloon & string