Impulsive Force

LESSON PLAN USING THE 4-PHASE TEACHING MODEL/LEARNING CYCLE Subject Class Date Time No. of students Learning Area Learning Objective

: : : : : : :

Physics Form 4 BESTARI 25 May 2009 9.00am-9.30am (30 minutes) 25 students Forces and Motion Analyzing Impulse and Impulsive Force

Learning Outcomes

:

At the end of the lesson, a student is able to:

A

Master content knowledge

a. State the definition of impulse and impulsive force in their own word.

b. Relate the impulsive force with rate change of momentum. c. Calculate one questions related impulse and impulsive force. B

Master Scientific Skills/TSTS a. Observing and inferring what will happen to the car when the car involved an accident b. Predicting what will happen to the car when the car collide c. Solving a problem based on the daily life situation.

C

Demonstrate Scientific Attitudes and Noble Values a. Have critical and analytical thinking. b. Dare to try. c. Being flexible and open-minded.

Scientific Concepts: a.

b.

Impulsive force is the rate of the change of momentum Acceleration= change of momentum = final momentum – initial momentum Time taken time taken

Materials, equipments and resource materials: Egg, container, water, slide power point,

Consideration of Safety Precautions: None

Prior Knowledge: Students have the idea about the momentum and application momentum in daily life.

Phase

Introduction/ Eliciting Ideas (5 minutes)

Content

Definition of force and momentum

Teaching and Learning Activities Teacher Activities Student Activities Recall what students have Students learnt about force respond to and momentum teacher’s from previous questions lesson.

Notes

Strategy/Technique: Whole class Q&A

Shows a picture of F1 car Structuring/ Restructuring of Ideas (15 minutes)

Definition of impulsive force and impulse State that impulsive force =

change of momentum time

Impulse : Ft = change of momentum

The contact time on impact is affected by the hardness of surface. The harder the surface, the shorter the contact time on impact When time is shortest, the force of impact will larger.

Ask student what is the definition of impulsive force? Shows the demonstration: Falling egg Ask a student: what inference that they can make from the demonstration show egg falling on harder surface and soft surface? Ask a student: Which experiences a greater force of impact? Ask a student

Strategy/Technique: An inquiry activity. Student observe and inferring to the demonstrati on.

Student constructs their definition by write on whiteboard.

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what inference that they can make from time taken with the force of impact? Ask a student to construct an equation of impulsive force with the change of momentum and time. What is impulse? Application of Ideas (5 minutes)

One problem involving the use of impulsive force = change of momentum time

Strategy/Technique: Show the problem based on the impulsive force of tennis player in the slide.

Students form a group to discuss the question

Whole class Q&A

Student solve a problem in a white board Reflection/ Closure (5 minutes)

Impulsive is the rate of change in momentum Impulsive force =

change of momentum time

Let students conclude by stating the main ideas and relating to students initial ideas using concept maps.

Strategy/Technique: Student creates a concept maps of impulsive

An inquiry activity.

Impulse and impulsive force? A tennis player hits an oncoming ball with a mass of 0.2kg and a velocity of 20ms-1. The ball rebounds with a velocity of 40ms-1. The time taken un the collision between the ball tennis racket is 0.01s. a) What is the impulse experienced by the ball? b) What is the impulsive force exerted on the tennis ball? c) If the tennis ball which has a velocity of 20ms-1 is hit by the racket with a force of 50N and the ball rebounds with a velocity of 5ms-1. What’s is the time of collision between the ball and he racket? Answer Impulse equals change in momentum. The ball's momentum change is m(v1 + v2) = 0.2*60 = 12 N-s Impulse also equals average force times time, so 12 = F*t = F*0.01, F = 1200 N Momentum change = 25*0.2 = 5 N-s = F*t. For F of 50 N, t = 5/50 = 0.1s Answer impulse is the change in momentum of the ball therefore mv1 - (-mv2)= impulse.. mv2 is -ve because of cartesian sign convection => a) m[v1 + v2]= 0.2 [20 * 40]= 0.2 * 800= 160 kg m/s b) impulse= F * t where f is force and t is time of collision 160 = F*0.01 F= 16000 newton c) Impulse = change in momentum F * t = p2 - p1 t = m [v1 - (-v2)] / F t = 0.2 [20 + 5] / 50 t = 0.1 sec