Newton’s Laws

Leges Motus The original text was written in Latin. Way loosely translated they are… –I. Things keep doing what they are doing until they get messed with. –II.  F=ma –III. You push on it, it pushes back just the same. Let’s explore each a little further.

First Law Inertia Just find the mass

Second Add all the forces, direction is important, do one equation for each dimension (horizontal and vertical)

Third Equal and opposite reaction. Every force on one object is accompanied by an equal and opposite force on the other object. You might need to sum forces on two objects to solve the problem.

Common Forces Name some… Gravity (weight=mg) Normal (perpendicular to surface) Tension (pull) Thrust (push) Friction (rub) Springs (Hooke’s Law)

Weight What is the weight of a 10 kg mass on earth? W=mg W=10(9.8)=98 N

Tug-o-war Five guys with a total mass of 800 kg tug against 6 others of total mass 790 kg. The five can pull with 2000 N. The team of six pulls with 2050 N. The mass of the rope used is 60 kg. What is the acceleration of the mass of people and rope?

Tug-o-war 2000 N2050 N Good time to talk Newton’s Third Law. The teams pull against the rope. In order to do this they must plant their feet into the ground. The force they exert on the ground is equal and opposite the force the ground exerts on them. The force they exert on the ground is directed toward the center. So the ground pushes them backward. 60 kg 800 kg790 kg

Airplane launch What force is necessary to accelerate a 23,000 kg airplane at 15.0 m/s 2 ?

Kinematics! Don’t forget them

…Airplane launch… A 15,000 kg airplane is accelerated to 75 m/s over a displacement of 65 m. What net force was required? 649,000 N

Bowling ball launch! How many seconds will it take to reach a speed of 12 m/s when a force of 2400 newtons is applied to a mass of 10 kg initially at rest? F=ma… a=F/m… v=v 0 +at… t=(v-v 0 )/a…= 0.05 seconds

“Traffic Light”   m mg T2T2 T1T1

Block on a Plane m