OUTCOMESASSESSMENT CRITERIA  After working through this unit, you should be able to:  Show the understanding of Newton's law.  Solve all the problems given after the lesson.  Define all the underlined words  Describe all the Newton’s three laws.  Use the real life examples to apply all the three laws.  Set your own problems regarding to the three laws and be able to solve them

Newton’s first law of motion A body will remain at rest or continue with a uniform velocity unless it is acted upon by an External Resultant force(s)

A body remaining at rest

External Resultant force(s) acting on the body

The law, therefore describes the tendency of a body to continue moving at a constant velocity in the absence of the resultant force. The law also describes the tendency of a body to remain at rest in the absence of the resultant force. From this law it can be seen that a body has a natural tendency to resist any change to its state of motion. And this resistance is known as Inertia

A resultant force acting on a body accelerates the body in the direction of the force. The acceleration is directly proportional to the resultant force and inversely proportional to the mass of the body.

Newton’s second law states the relationship between the force(F), the mass(m) being accelerated and the acceleration(a). F=ma Where F= the force(measured in N) and m= the mass(measured in kg) and a= the acceleration( measured in m-s²). It goes a step further and deals with the motion of the bodies that accelerates as a result of a resultant (unbalanced) force

Force is a vector quantity. It has a specific direction. When a force(resultant) acts on a body, it accelerates in the direction of the body. Hint(s) on problem solving: Draw a force diagram of all the forces acting on the body. Always chose direction. Take your time and double check your answer.

Make it a point that your final answer have unit. For example, where F= 2N and acceleration= 10 m-s² and asked to calculate the mass of the body. F= ma therefore 10= m2 m= 5 kg

Use Newton’s laws to explain the following: (a)A person standing inside a bus, must hold on to the seat to prevent himself from falling when the bus start moving. (b)It is advisable that the driver of a car should wear a safety-belt in case he gets involved in a head-on collision.

Solution(s): (a) According to Newton first law, the person will maintain his state of rest: the seat thus exerts a resultant force F on the person in order for him to accelerate forward (Newton’s second law)

(b) According to Newton’s first law, the driver will maintain his state of motion in a straight line, that is through the wind screen! The safety-belt exerts a resultant force F on the person in the opposite direction as the motion of the car. The driver then will experience a negative acceleration and come to rest (Newton’s second law)

 A container, standing on the floor, has a mass of 25 kg. the frictional force between the floor and the container is 15 N. if a horizontal force of 65 N acts on the container, calculate its acceleration. (see the figure on your right)

Remember : The direction of the frictional force is always opposite to the direction of motion of the body.

 Firstly, calculate the resultant force  Apply Newton 2 nd law.  Substitute correct values.  a is a vector- the acceleration and the force is in the same direction. F(res)= =50 F(res)=ma 50=25*a a= 2 m-s² to the right

 If a body A exerts a force on a body B, then body B exerts an equal force on body A, but in a opposite direction.

Take the following into consideration:  Newton’s third law has no connection with the other two laws of motion.  All forces in nature occurs in pairs.  The forces act simultaneously on two different bodies and therefore cannot be regarded as balanced forces.  The force are of the same magnitude.

 Application of Newton’s 3 rd Law.  For a person pushing a bus, the reaction to this force would be an equal but opposite force exerted by the car on the person Opposite force from the bus Opposite force from the person

 However, although of the same magnitude, the two forces are not in equilibrium because they act on different bodies.  If the two bodies are isolated, it is clear that only one force acts on the car, which therefore must be the resultant force causing the car to accelerate.

(a) Define the term inertia. (b) Describe the three Newton’s law of motion. (c) The acceleration of the body is……the resultant force acting on the body 1. Numerically equal to 2.independent of 3. Inversely proportional to 4. directly proportional to

(d) A dead person, lying on the floor, has a mass of 25 kg. The frictional force between and the dead person is 15 N. if a horizontal force of 65 N acts on the dead person, calculate the accelerate. (e) The backward force of an athlete’s feet against the ground, is equal to the forward force of the ground against the feet. Explain why the athlete would move forward while the earth does not move backward (eye the below diagram)

(a) Inertia- the natural tendency of the body to resist any change to its state of motion. (b)- Newton’s first law- a body will remain at rest or continue with a uniform velocity unless it is acted upon by an external force. -second law- A resultant force acting on a body accelerates the body in the direction of the direction. The acceleration is directly proportional to the resultant force and inversely proportional to the mass of the body.

-third law- if a body A exerts a force on body B, then body B exerts an equal force on body A, but in an opposite direction. (c) D- Newton's 2 nd law (d) See example number 3 on your notes (e) From Newton’s third law: in terms of the athlete's action- the force of the athlete against the earth (F) to the left. And in terms of reaction – the force of the earth against the athlete(F1) to the right.

Not forgetting that F and F1 are equal but in opposite direction.