Forces Force A push or a pull that

Forces

Force • A push or a pull that may cause an object’s motion to change! – Unit force is the Newton(N)! – It is a vector quantity. • Direction is important!!

• Do forces have to be “in contact” in order to have an affect on another object?

Balanced vs. Unbalanced Forces” • Balanced forces—forces • Unbalanced forces— that are equal in forces that are not magnitude, but equal in magnitude and opposite in direction!! opposite in direction! – Will not cause a change in the motion of the object!! – Will cause a change in the motion of the object!!

Are the forces Balanced or Unbalanced? Balanced Unbalanced

Balanced or Unbalanced: A. Balanced B. Unbalanced

Balanced or Unbalanced: A. Balanced B. Unbalanced

Net Force(Fnet) • Sum of all forces acting on an object. • If there is a net force acting on an object, the velocity of the object will change!!

Balanced or Unbalanced? Find the Net Force Unbalanced FNet = 30 N left

Balanced or Unbalanced? Find the Net Force Balanced FNet = 0 N

Balanced or Unbalanced? Find the Net Force Unbalanced FNet = 10 N Right

Balanced or Unbalanced? Find the Net Force Unbalanced FNet = 130 N down

Balanced or Unbalanced? Find the Net Force unbalanced FNet = 360 N right

Find the Net force in the diagram below: A) 120 N right B) 120 N left C) 20 N right D) 20 N left

Determine the Net Force: A) 10 N right B) 150 N right C) 160 N right D) 150 N left

Newton’s st 1 Law of Motion • also known as the “Law of Inertia”. – Inertia—tendency of an object to resist change in motion. • Explain? ? ? • What does inertia depend on? • 1 st Law--An object at rest stays at rest and an object in motion stays in motion, unless acted on by some unbalanced force!

More thoughts on Inertia: What gives an object inertia? ?

Inertia(cont): Mass gives an object inertia!! It is easier to change the motion of a small object than it is to change the motion of a larger object!! Does anything else affect inertia?

I must think about balancing my bike!!! Inertia(cont. ) Think about a bicycle!! Ever tried to balance on a bike while standing still? Was it easy? Was it impossible?

I must think about balancing my bike!!! Inertia(cont. ) When you ride your bike down the road, how many of you think to yourself, “I must balance my bike, I must balance my bike!!” What’s the difference? Click me #1 Click me #2

Newton’s 1 st Law of Motion(cont. ) • If you roll a ball across the floor, why does it eventually come to a stop. – Is there a force acting against it? – If so, what is it? • Friction—force that opposes motion. – Always acts in the direction opposite of motion. Anything slowing this Coke as it slides across the bar?

Newton’s nd 2 Law of Motion • called the “Law of Acceleration”. • Relates force, mass, and acceleration. • Force and acceleration directly related. • Mass and acceleration inversely related.

Newton’s 2 nd Law of Motion(cont. ) F=ma • Where: ØF = force in Newton’s(N) Øm = mass in kilograms(kg) Øa = acceleration in m/s 2

Ex. What force is required to accelerate a 1500 kg car by a rate of 1. 5 m/s/s? Given: m = 1500 kg a = 1. 5 m/s/s F=? F=ma F = 1500 kg(1. 5 m/s/s) F = 2250 N

Ex. A force of 290 N is applied to a 20 kg rock. At what rate will the rock accelerate? Given: m = 20 kg a=? F = 290 N F=ma a = 14. 5 m/s 2

Ex. A force of 140 N is applied to a mover’s dolly to accelerate a load of Cokes across the grocery store at 3 m/s 2. What is the mass of the load of Cokes? Given: F = 140 N a = 3 m/s 2 m=?

A force is applied to accelerate a 50 kg mass at a rate of 2. 5 m/s/s. What force is required? A. B. C. D. 20 N 25 N 120 N 125 N

A 250 N is applied to a 12 kg mass. At what rate will the object accelerate? A. 3000 m/s/s B. 240 m/s/s C. 20. 8 m/s/s D. . 05 m/s/s

Newton’s rd 3 Law • For every action, there is an equal but opposite reaction. Forces always occur in pairs!!

Which of the following scenarios does not represent Newton’s 3 rd Law? A. A rocket being launched into space. B. A book resting on a desk. C. A person paddling a canoe. D. A large force pushing on a small mass, causing it to accelerate.