Newton’s Laws of Motion Dynamic dynamics and unexpected returns Chapter 3

Sir Isaac Newton Determined many physical laws based on mathematics. His book, Principia, revolutionized the fields of both science and mathematics

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 –Dependent on mass

Newton’s 1 st Law of Motion

Which has more inertia? 1. An empty dump truck 2. A full dump truck

Which has more inertia? 1. A quarter 2. A dime

Which has more inertia? 1. A freight train 2. A full dump truck

Which has more inertia? 1. A freight train 2. A cargo plane

Which has more inertia? 1. An empty dump truck going 170 km/h 2. A cargo plane sitting on the runway

Newton’s Second Law of Motion Force equals mass multiplied by acceleration F = ma –Force is any push or pull that can affect motion –Mass in kg, acceleration in m/s 2 –Newtons: 1N = 1kgm/s 2

Newton’s 2 nd Law of Motion

What is the force applied by a mass of 2 kg with an acceleration of 6 m/s 2 ? 1. 6 N 2. 3 kg●m/s kg●m/s 2

What is the acceleration of a mass of 6 kg applying a force of 24 N? 1. 4 m/s m/s m/s 2

What is the force applied by the acceleration of a 3.5 kg mass to 7 m/s 2 ? 1. 2 N kg●m/s kg ●m/s 2

What mass is required to apply a force of 28 N after an acceleration of 7 m/s 2 ? kg 2. 4 kg kg

What acceleration would cause a 12 kg mass to produce a force of 90 kg●m/s 2 ? N m/s m/s 2

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 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? ,616 N ,616 N 3. 0 N

What would the net force be if two players kick a soccer ball from opposite directions according to the diagram? N, to the left N, to the right 3. 0 N N, upwards

What would the net force be if you pushed a hockey puck with 200 N? 1. 0 N N against the push 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

Newton’s 3 rd Law of Motion

Good Examples Rocket engines Firing a gun Jumping off of a johnboat

Forces and Vectors

Gravity Gravity is a force of attraction between all objects of mass. Depends on: –the distance between the masses “inverse square” law –the size of the masses Often as a percentage of the whole

Weight Weight is the force of attraction caused by gravity acting on a mass. F w = mg The g means local gravity –on Earth, g = 9.8m/s 2

Gravity

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? N N N

If an object weighs 397 N, what is its mass? kg kg kg

If an object weighs 1100 N but has a mass of 125 kg, which planet is it on? 1. Venus, g = 8.8 m/s 2 2. Mars, g = 3.7 m/s 2 3. Jupiter, g = 24.8 m/s 2

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

Types of Friction Sliding Friction –When two surfaces slide along each other –Most resistive friction –Can lead to buildup of heat

Types of Friction Rolling Friction –When an object or surface rolls along another –Less resistive than sliding, more resistive than fluid

Types of Friction Fluid Friction –When a surface slides along a fluid (gas or liquid) –Least resistive friction Lubrication –Air resistance

What type of friction is exhibited by your shoes on the ground? 1. Sliding 2. Rolling 3. Fluid 4. Air Resistance 5. None of the above

What type of friction is exhibited by a lubricant? 1. Sliding 2. Rolling 3. Fluid 4. Air Resistance 5. None of the above

What type of friction is exhibited by the wheels on a cart? 1. Sliding 2. Rolling 3. Fluid 4. Air Resistance 5. None of the above

What type of friction is exhibited by your fingerprints? 1. Sliding 2. Rolling 3. Fluid 4. Air Resistance 5. None of the above

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

What is the momentum of a 210 kg hog running at 12 m/s? kg ● m/s kg ● m/s kg ● m/s

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 m 1 v 1 +m 2 v 1 = m 1 v 2 +m 2 v 2

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.