Momentum and Energy

ISCI 2002

1. “Inertia” in motion

2. Momentum = (mass) x (velocity)

3. Greater the mass > Inertia > momentum of the object

Objects in Motion - MomentumObjects in Motion - Momentum

1. If the mass or velocity of an object changes – momentum changes

2. Acceleration is the result

3. __________ produces acceleration. Which of Newton’s Laws apply?

4. What else affects acceleration? • Time – how long the force is applied

5. Impulse = force x time interval• Impulse = change in momentum or Ft = Δmv

Changes in Momentum Changes in Momentum

1. If a physical quantity remains unchanged – ‘conserved’

2. In the absence of an external force, the momentum of a system remains unchanged.

Conservation of MomentumConservation of Momentum

1. In the exploding cannon demonstration, total system momentum is conserved. The system consists of two objects - a cannon and a tennis ball. Before the explosion, the total momentum of the system is zero since the cannon and the tennis ball located inside of it are both at rest. After the explosion, the total momentum of the system must still be zero. If the ball acquires 50 units of forward momentum, then the cannon acquires 50 units of backwards momentum. The vector sum of the individual momenta of the two objects is 0. Total system momentum is conserved

Momentum Conservation Momentum Conservation

Conservation of Momentum Conservation of Momentum

When you lift a sphere on one side and let it go (Figure 1), its energy gets transferred from the original metal sphere, through the ones in the middle, all the way to the furthest sphere from the original (Figure 2). The last sphere to receive the energy continues with the momentum of the original sphere, until gravity overcomes its inertia and pulls it down (Figure 3). The energy is then transferred back through the spheres in the middle to the first sphere (Figure 4), where the cycle starts all over again

This phenomenon of forces being exerted, and momentum being transferred is known as Conservation of Momentum. There are many games that are designed with this phenomenon in mind. Eight-ball is one of them! Go to a pool table, and the object is to hit the correct balls in chosen pockets using the momentum of the cue ball, or the cue ball in combination with others. It takes into account conservation of momentum, as well as mass, acceleration, and force (Newton’s second law of motion!).

This phenomenon of forces being exerted, and momentum being transferred is known as Conservation of Momentum. There are many games that are designed with this phenomenon in mind. Eight-ball is one of them! Go to a pool table, and the object is to hit the correct balls in chosen pockets using the momentum of the cue ball, or the cue ball in combination with others. It takes into account conservation of momentum, as well as mass, acceleration, and force (Newton’s second law of motion!).

This phenomenon of forces being exerted, and momentum being transferred is known as Conservation of Momentum. There are many games that are designed with this phenomenon in mind. Eight-ball is one of them! Go to a pool table, and the object is to hit the correct balls in chosen pockets using the momentum of the cue ball, or the cue ball in combination with others. It takes into account conservation of momentum, as well as mass, acceleration, and force (Newton’s second law of motion!).

1. Collisions • Elastic vs inelastic

2. Net momentum before = net momentum after

3. Case of the ‘coupled’ train cars.

Collisions Collisions

M = 1.0 kg V = 2.0 m/s

M = 1.5 kg V = 0 m/s

V = ??

Elastic CollisionElastic Collision

The gray rubber ball collides with the static red rubber ball.

Here momentum and kinetic energy is conserved.

Almost no energy is lost to sound, heat or deformation.

The KE from the first ball is transferred to the second ball

KE

1. Work = Force x Distance

2. Force is exerted, and something is moved!

3. Unit = N x m or Joule

4. Power = work done / time interval

5. Unit = Watt

Work and Power Work and Power

Previously studied ‘heat’ energy.

• Different forms of energy• Sound, electricity, radiation, etc.

• Objects may: 1. Store Energy (PE) or possess movement (KE)

2. Potential Energy – Energy of Position• Gravitation Potential Energy (mgh)

3. Kinetic Energy – Energy of Motion • Transfer; transformation • KE = ½ mv2

Energy Energy

• Machines • Multiply forces; change direction of a force• Conservation of Energy is the key

• Work Input = Work Output • (Force x distance) = (Force x Distance)

• A car jack • A girl pushes the handle with a force of 50 N (input force) a

distance of (input distance) 0.25 cm. The car (output force) weighs 5000 N rises a distance of 0.25 cm (output distance).

• Car rises with 100 times the force!• Multiplies the initial force.

Energy, Work and Simple Machines Energy, Work and Simple Machines

Mechanical Advantage Mechanical Advantage

• Simple machines • Same energy input, but increases work • More efficient

• Efficiency = work done/energy used

Efficiency Efficiency