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Physic form4 Chapter 2 Forces and motion

2.5 FORCE

Prepared by Nuridah Binti ZaimiSMK KepongWhat is Force?A push or pull that acts on an objectCan cause a resting object to moveCan accelerate a moving objectBy changing its speed or direction

Give an example of activity involving forces in your daily life1. Lifting object

2. Pulling off the ring of a soft drink tin.

3. Kicking a football4. Stretching the chest expander

5. Pressing the switch

What is the effect Force?A force change the shape and size of an object.A force change the original state of motion (either at rest or on motion) of an object.A force change the shape and size of object.

A force change the original state of motion (either at rest or on motion) of an object

Relationship between acceleration, mass and forces.

Experiment to find the relationship between force, mass & Acceleration.Experiment 1.1acceleration & Force when mass is constantExperiment 1.2acceleration & mass when force is constant.

inferencea & FThe acceleration produced by an object depends on the net force applied to it.a & mThe acceleration produced by an object depends on its mass.Hypothesisa & FThe acceleration of the object increase when the force applied increases.a & mThe acceleration of the object decreases when the mass applied increases.resulta & Fa & m

Acceleration, aForce, FThe acceleration of an object is directly proportional to the force applied if the mass is constant.The acceleration of an object is inversely proportional to it mass when the force acting on its is constant.From previous experiment

Newtons 2nd Law of Motion The acceleration of an object is equal to the net force acting on it divided by the objects mass

Newtons 2nd Law of Motion

How is force measured?Unit of Force Newton (N)1 kg to accelerate 1 m/s2

How is force represented?Use arrowsDirectionStrengthLength represents strength or magnitude

The scale with more apples, greater mass, has a longer arrow. The arrow is pointed downward due to mass is below the balance pulling downwards.

Balanced vs. Unbalanced ForcesBalancedCombine to produce a net force of zeroNo change in the objects motionUnbalancedNet force equals the size of the larger force minus the size of the smaller forceNet force does not equal zeroCauses an object to accelerate

FrictionForce that opposes the motion of objects that touch as they move past each otherActs at the surface where objects are in constant.

Balanced forces

Balanced force

Balanced force when the forces acting on an object are balanced, they cancel each other out. (that is net force = 0).

The object remain at rest or moves at constant velocity when there is no force acting on it.

Example

Unbalanced force/resultant force when the forces acting on an object do not cancel out each other.

The object will accelerate in the direction of the net force.

The net force is known as the resultant force.

Lets solve this problemNewtons 2nd Law of Motion a= F/m = 60.0 N/40.0 kg = 1.50 m/s2

1.A boy pushes forward a cart of groceries with a total mass of 40.0kg. What is the acceleration of the cart if the net force on the cart is 60.0N?

2.What is the upward acceleration of a helicopter with a mass of 5000kg if a force of 10,000N acts on it in an upward direction? a=F/m = 10000 N/5000 kg = 2 m/s23.An automobile with a mass of 1200kg accelerates at a rate of 3.0m/s2 in the forward direction. What is the net force acting on the automobile? (Hint: Solve the acceleration formula for force.)

A =F/m F=ma = 1200 kg(3.0 m/s2)= 3600 N

4.A 25-N force accelerates a boy in a wheelchair at 0.5m/s2 What is the mass of the boy and the wheelchair? (Hint: Solve Newton's second law for mass.)

a=F/m m=F/a = 25 N/0.50 m/s2 = 50 k/=gSection 2 Practice Problems 5. During a test crash, an air bag inflates to stop a dummy's forward motion. The dummy's mass is 75kg. If the net force on the dummy is 825N toward the rear of the car, what is the dummy's deceleration? a=F/m = 825 N / 75 kg = 11 m/s2

6.A bicycle takes 8.0seconds to accelerate at a constant rate from rest to a speed of 4.0m/s. If the mass of the bicycle and rider together is 85kg, what is the net force acting on the bicycle? (Hint: First calculate the acceleration.)a=(vf-vi)/t = (4.0 m/s) / 8.0 s = 0.50 m/s2F=ma = 85 kg x 0.50 m/s2 = 43 NPop quiz.Take out 1 piece of paper and calculator..

Are you ready????

Question 1.Find the acceleration of the objects.

F = 10 N Frictionless surface5 kgQuestion 2Find the acceleration of the objects.

FR = Friction forceF = 45 NFR = 15 N3 kgQuestion 3Find the value of F.

F

FR = Friction forcea= 4 m/s2FR = 5 N10 kgQuestion 4Calculate the value of m.

F=60N

FR = Friction forcea= 2 m/s2FR = 10 NmQuestion 5 A 10 kg object accelerate from rest to 5 m/s in 2 s. What is the net force acting on the object?

Question 6 A force of 10N acts on a 2 kg stationary object. Calculate the distance travelled by the object in 5 s.Question 7 An object with a mass of 5 kg moves at a constant velocity when it is pulled by a horizontal force of 5N on a level surface. What is the acceleration of the object if the object is pulled with a force of 25N?