Newton’s Laws of Motion Force, gravity, projectiles, friction, & momentum

Sir Isaac Newton Determined many physical laws based on mathematics. His book, Principia, revolutionized the fields of both science and mathematics. He did a great job of explaining effects that seemed to have no causes.

Four Basic Types of Forces Gravity Electromagnetic Strong nuclear Weak nuclear

Newton’s First Law of Motion Inertia - An object at rest will remain at rest, and an object in motion will remain in motion unless acted upon by an outside force. How does mass effect inertia?

Which has more inertia? An empty dump truck A full dump truck A quarter A dime A freight train

Which has more inertia? A freight train A cargo plane An empty dump truck going 170 km/h A cargo plane sitting on the runway

Newton’s Second Law of Motion Force equals mass multiplied by acceleration F = m•a Force is any push or pull that can affect motion Mass in kg, acceleration in m/s2 Newtons: 1N = 1kg•m/s2

What is the force applied by a mass of 2 kg with an acceleration of 6 m/s2? 3 kg●m/s 12 kg●m/s2

What is the acceleration of a mass of 6 kg applying a force of 24 N? 4 m/s2 144 m/s2 0.25 m/s2

What is the force applied by the acceleration of a 3 What is the force applied by the acceleration of a 3.5 kg mass to 7 m/s2? m a F 2 N 24.5 kg●m/s2 0.5 kg ●m/s2

What acceleration would cause a 12 kg mass to produce a force of 90 kg●m/s2?

Balanced v. Unbalanced Forces Balanced forces are equal and opposite on the same object Balanced forces result in NO acceleration Equilibrium Unbalanced forces are added geometrically The Resulting or Net Force (Fn) always results in an acceleration

Showing “Equal and Opposite” The observer determines the direction of motion Directions opposite that motion can be considered NEGATIVE Because the direction is considered negative, the forces can be considered negative

What would the net force be if you pushed against the wall with 122,616N?

What would the net force be if two players kick a soccer ball from opposite directions according to the diagram? 60 N, to the left 60 N, to the right 0 N 180 N, upwards

What would the net force be if you pushed a hockey puck with 200 N? 200 N against the push 200 N in the direction of the push

Newton’s Third Law of Motion For every action, there is an equal and opposite reaction (These forces act on two different objects, so they are not balanced forces.)

Which Law???

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Gravity Any two masses exert an attractive force on each other. Depends on: the distance between the masses the size of the masses

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 on Earth A gravitational force exists between all matter in the universe. This is a huge range. The force of gravity on Earth pulls down.

Projectiles Because of Earth’s gravitational pull and their own inertia, projectiles follow a curved path due to horizontal and vertical velocities. When you release a ball, the ball moves downward because of gravity, but the horizontal speed remains the same. A thrown ball will land at the same time as a dropped ball because the velocity components are independent. http://phet.colorado.edu/en/simulation/projectile-motion

Weight Weight is the force of attraction caused by gravity acting on a mass. Fweight = m X g The g means local gravity On Earth, gravity = 9.8m/s2 Fw m g

Weight v. Mass We use weight and mass interchangeably because the only comparison we have is the Earth’s gravity. Weight will change based on local gravity; NASA has to take this into effect

How much does a 25 kg object weigh in Newtons? Fw 245 N 2.6 N 0.392 N Remember: gravity = 9.8m/s2

If an object weighs 397 N, what is its mass? Fw 0.02 kg 3890.6 kg 40.5 kg

If an object weighs 1100 N but has a mass of 125 kg, which planet is it on? Fw Venus, g = 8.8 m/s2 Mars, g = 3.7 m/s2 Jupiter, g = 24.8 m/s2

Friction Friction is the force that opposes all motion. A moving object will always lose energy to friction.

3 Types of Friction more 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 less

Friction of Unmoving Objects Static friction results when the surfaces of two objects are at rest relative to one another and a force exists on one of the objects to set it into motion relative to the other object. https://www.youtube.com/watch?v=AX_lCOjLCTo Under a microscope we see that materials that feel smooth are rough. Areas where the bumps of materials stick together are called microwelds and are the source of friction.

Air Resistance The amount of air resistance on an object depends on the speed, size, and shape of the object. There is no air resistance in a vacuum.

What type of friction is exhibited by your shoes on the ground? Sliding Rolling Fluid Air Resistance None of the above

What type of friction is exhibited by a lubricant? Sliding Rolling Fluid Air Resistance None of the above

What type of friction is exhibited by the wheels on a cart? Sliding Rolling Fluid Air Resistance None of the above

What type of friction is exhibited by your fingerprints? Sliding Rolling Fluid Air Resistance None of the above

The Big “Mo” Momentum is the product of an object’s mass multiplied by its velocity. p = m • v Momentum = mass X velocity

What is the momentum of a 210 kg hog running at 12 m/s? Fw p 17.5 kg●m/s 2520 kg●m/s 0.057 kg●m/s m m g v

Law of Conservation of Momentum Momentum can not be created or destroyed under normal circumstances Momentum can be changed from one form to another Total momentum before a change must equal total momentum after a change Ex. truck of gravel coming to a stop, pieces of a dropped light bulb

Law of Conservation of Momentum Formula m1v1+m2v1 = m1v2+m2v2

Momentum Demonstrations https://www.youtube.com/watch?v=W9EqU1_DXUw OR https://www.youtube.com/watch?v=W9EqU1_DXUw What if Earth stopped rotating? https://www.youtube.com/watch?v=K0-GxoJ_Pcg

Conservation of Momentum and Newton’s Laws An untethered astronaut is stranded away from his spaceship while working on a satellite in space. The only equipment he has is all the tools he was using to repair the satellite. Write a short narrative of how you think he can get back to his spaceship.