Chapter 4: Linear Kinetics

Objectives:
• Explain Newton's three laws of motion
• Apply Newton's second law of motion to determine the acceleration of an object if the forces acting on the object are known
• Apply Newton's second law of motion to determine the net force acting on an object if the acceleration of the object is known
• Define impulse
• Define momentum
• Explain the relationship between impulse and momentum
• Describe the relationship between mass and weight

Isaac Newton (1642-1727) Newton's Laws of Motion

Football against Eli Herring and Usain Bolt Eli: 157 kg at 8.0 m/s
Usain: 94 kg at 12.35 m/s

Conservation of Momentum
L=mv

Linear Kinetics: Explaining the Causes of Linear Motion

Objectives:

Money experiment (penny mass=2.5g, nickel=5.0g)

Elastic collisions: maua + mbub= mava + mbvb

Elestic versus inelastic collisions

Coefficient of Restitution  Inelastic collisions: maua + mbub= mava + mb [e(ua - ub) + va]

Force affects motion

Measuring Ground Reaction Forces

Ground Reaction Forces in Running

How Do Weight and Inertia affect preferred movement?
Lunar Locomotion

F=ma Buildup of velocity in the shot put (Download Video)

When Force is Changing: Impulse = Favg Δ t
How do we calculate impulse?

Soccer Kick Example (video)

How does this work in a spreadsheet?

Summary of Newton's Laws
First law: Inertia (resistance to a change in motion)
Second law: F=ma
Third law: Action-reaction

F=G(m1m2/r2)

G=6.67300 x 10-11m/kg/s2
Mass of earth = 5.9742 × 1024 kg
Radius of earth = 6378.1 km

G(mearth/(rearth)2)=?

F=ma or W=mg

How much does an astronaut weigh?

Questions:
1. Can a body be moving if no external forces are acting upon it?
2. Can a body change its direction of motion if no external forces act on it?
3. Can a body be moving with constant velocity if external forces are acting on it?
4. If you pull on a tug of war rope with a force of 50 lb, how much force does the rope exert on you?