NEWTON’S SECOND LAW OF MOTION (Ch. 3-1) FORCE NEWTON’S SECOND LAW OF MOTION (Ch. 3-1)

Objectives Explain how force, mass, and acceleration are related to Newton's second law of motion. Describe the three different types of friction. Define terminal velocity and describe the effects of air resistance on a moving object. CLE 3202.3.2 Investigate and apply Newton’s three laws of motion.

A. Force and Motion are connected An object will have greater acceleration if a greater force is applied to it. When a net force acts on an object, the object will accelerate in the direction of the net force.

3. Acceleration is determined by two factors: the size of the force and the mass of the object

4. A larger force results in greater acceleration.

5. A larger mass needs a greater force.

4. Newton’s Second Law of Motion (law of unbalanced forces)

B. Newton’s 2nd Law of Motion When an unbalanced force acts on an object, the object accelerates in the direction of the applied force.

Connects force, mass and acceleration in the equation acceleration equals net force divided by mass.

F= force (Newton) (N) f = ma

m= mass kg g m = f/a

a= acceleration m/s2 a=f/m

F = ma F m a A. Newton’s Second Law F m F: force (N) m: mass (kg) a: accel (m/s2) 1 N = 1 kg ·m/s2

Equations f = m × a m = f ÷ a a = f ÷ m f Divide m a Multiply

1 Newton (N) is the amount of force needed to move 1 kilogram of mass

C. Friction - force that opposes motion between two surfaces that are touching each other. 1. The amount of friction depends on: the kinds of surfaces. the force pressing the surfaces together. 2. Microwelds, areas where surface bumpers stick together, are the source of friction.

Sticking Together The larger the force pushing the two surfaces together is, the stronger these microwelds will be, because more of the surface bumps will come into contact. To move one surface over the other, a force must be applied to break the microwelds.

3. Friction between two surfaces that are not moving past each other is called static friction. That force is the friction due to the microwelds that have formed between the bottom of the box and the floor.

4. Sliding friction - force that opposes the motion of two surfaces sliding past each other Pushing together, the box moves. Together you and your friend have exerted enough force to break the microwelds between the floor and the bottom of the box.

Sliding Friction

friction between a rolling object and the surface it rolls on. 5. Rolling Friction - friction between a rolling object and the surface it rolls on.

1. Air resistance opposes the force of gravity. D. Air resistance – the force air exerts on a moving object. 1. Air resistance opposes the force of gravity. 2. It acts in the opposite direction to the objects motion. 3. The amount of air resistance depends on an objects speed, size, shape, or density.

Air Resistance Air resistance, not the object’s mass, is why feathers, leaves, and pieces of paper fall more slowly than pennies, acorns, and apples.

What would happen to an object dropped on the moon?

Terminal velocity - the point when a falling object stops accelerating. Forces on a falling object are balanced, and the object falls with a constant speed. Example: parachute opening

Terminal Velocity Velocity at which an object is traveling when it stops accelerating

Discussion question: What three variables does a Newton’s second law of motion connect?

Question Answer What causes friction? Friction results from the sticking together of two surfaces that are in contact.

a D. Calculations F m F = ? F = ma m = 40 kg F = (40 kg)(4 m/s2) What force would be required to accelerate a 40 kg mass by 4 m/s2? GIVEN: F = ? m = 40 kg a = 4 m/s2 WORK: F = ma F = (40 kg)(4 m/s2) F = 160 N m F a

a D. Calculations F m m = 4.0 kg a = F ÷ m F = 30 N A 4.0 kg shotput is thrown with 30 N of force. What is its acceleration? GIVEN: m = 4.0 kg F = 30 N a = ? WORK: a = F ÷ m a = (30 N) ÷ (4.0 kg) a = 7.5 m/s2 m F a

Investigate and apply Newton’s three laws of motion. CLE 3202.3.2 Investigate and apply Newton’s three laws of motion. Objective: Explain how force, mass, and acceleration are related to Newton's second law of motion. Objective: Describe the three different types of friction. Objective: Define terminal velocity and describe the effects of air resistance on a moving object.

Objectives Explain how force, mass, and acceleration are related to Newton's second law of motion. Describe the three different types of friction. Define terminal velocity and describe the effects of air resistance on a moving object. CLE 3202.3.2 Investigate and apply Newton’s three laws of motion.