Lesson: IMPULSE & MOMENTUM

MOMENTUM

MOMENTUM

•The

word

momentum

(plural,

momenta)

is

Latin

and

means

“movement” or “inertia in motion”.
•Operationally,

momentum

is

defined as the product of mass and
velocity.
•It

is

expressed

in

units

like

kilogram - meter/second (kg.m/s) or
Newton - second (N.s).

Multiple Choice

What is the formula for momentum (p)?

• momentum = mass/velocity

• momentum = force x acceleration

• momentum = mass x velocity

Sample Problem 1

A 2,500 kg bus from Binangonan moves at 25 m/s to Cainta. What is the momentum of the bus?

Given:
•m = 2,500 kg
• v = 25 m/s

•Find: ρ = ?

Multiple Choice

Which has more momentum? (Remember: momentum = mass x velocity).

• 2,000 kg car with a velocity of 5 m/s

• 10,000 kg bus with a velocity of 1 m/s

• The car and the bus have the same momentum.

Which has more momentum?

✓

Multiple Choice

Which has more momentum?

• 30 kg player with a velocity of 2 m/s

• 60 kg referee with a velocity of 0 m/s

• The player and the referee have the same momentum.

✓

Multiple Choice

Which has more momentum, a heavy truck moving at 30 km/hr or a light truck moving at 30 km/hr?

• the heavy truck

• the light truck

• Both have the same momentum.

Open Ended

Consider riding a jeepney which is moving too fast and then a passenger asked for the jeepney to stop right away. Do you think the jeepney can stop right away? What will happen if the driver suddenly stepped on the break to stop the jeepney? (Write your answer in the box, even in Tagalog.)

The concept of momentum helps us to understand the tendency of moving objects to stop. These are the concepts you need to remember:
The FASTER the object is moving, the GREATER the momentum.
The GREATER the mass of an object, the GREATER the momentum.
The GREATER the momentum the HARDER the object to change motion or to stop.

Imagine playing the “Egg Volleyball” game (Fig.3), with teams consisting of 2 students. Each pair should have one large cloth or handkerchief. You will compete with the other team that is 3 meters away from you. Your goal is to have the egg travel back and forth from each pair of students without breaking the egg.

Multiple Choice

Do you think the handkerchief will be able to protect the egg from breaking?

• YES

• NO

The cushioning effect of the CLOTH allows the egg to have an increased time of impact therefore lessening the impact of force on the egg. The soft-landing surface lengthens the time of impact.

​On the other hand, the egg will break immediately when it hits the ground because of the hardness of the ground. This reduces impact TIMEleading to an increase in impact FORCE.

​To stop a moving object force is needed in a given period of time. The force and the time of impact changes the momentum. The change in momentum is called IMPULSE.

Multiple Select

What changes the momentum? (Select 2 answers.)

• force of impact

• velocity of impact

• time of impact

• acceleration

Multiple Choice

What is impulse?

• increase in velocity

• change in momentum

• decrease in acceleration

IMPULSE: CHANGE IN MOMENTUM​
Imagine yourself walking with a high momentum (with a high speed) trying to reach the classroom on time and then suddenly you bumped another student. You will suddenly stop and so your momentum changes. Your motion stopped because of an applied force when in contact with the other student. The change in momentum is known as Impulse.

​Impulse is known as the FORCE multiplied by the TIME of contact. In symbols:

I = Δρ  

where: I = impulse

      Δρ = change in momentum

​ I = Δρ  

since I = Ft

where:   F - force

  t - time

thus: Ft = mΔv

where:   m - mass

  Δv - change in velocity

Sample Problem:​
A force of 40 Newtons is exerted for 5 seconds on a moving cart. What is the impulse experienced by the cart?
Given: F = 40 N
t = 5 s
? = I (impulse)

​Solution:
I = Ft
= (40N)(5s)
= 200 Newton-second (Ns)

Multiple Choice

Which of the following statements is NOT true about momentum?

• It is a scalar quantity.

• A body at rest has zero momentum.

• Its basic unit is kg m/s.

• It is the product of mass and velocity.

Multiple Choice

Two marbles of equal mass are rolling towards each other. One is rolling at 7 m/sec and the other at 10 m/sec. The one rolling faster has a____ momentum and ___ impulse. It will surely knock the other one backwards.

• lesser, lesser

• greater, lesser

• lesser, greater

• greater, greater

Multiple Choice

Two identical cars are moving at different speeds and collided with a tree as shown in the figure. Car A caused greater damage on the tree than Car B. Why is this so?

• Car A is moving faster therefore its impact force is higher.

• Car A is moving slower therefore its impact force is higher.

• Car B is heavier than Car A so it creates less damage.

Multiple Choice

Which of the following statements is NOT true about impulse?

• Impacts can be decreased by increasing the time of contact.

• Force applied in a certain time causes a change in momentum.

• The impulse experienced by a body is equal to the change in its potential energy.

• In a collision, an object experiences a force for a specific amount of time that results in a change in momentum.

Multiple Choice

Why should the driver REDUCE speed when he/she sees a “curve” road sign?

• They need to reduce speed to prepare to stop to prevent accidents to happen.

• They need to reduce speed to gain more momentum to prevent accidents to happen.

• They need to reduce speed to lower the momentum to prevent accidents to happen.

• They need to reduce speed to increase the momentum to prevent accidents to happen.

The following pictures show the principle of increasing time of impact to reduce the force of impact EXCEPT: (Answer on the next slide.)

Multiple Choice

The following pictures show the principle of increasing time of contact to decrease the force of impact EXCEPT:

• A

• B

• C

• D