Forces and Net Force Pages 335 347 Objectives

“Forces and Net Force” (Pages 335 -347)

Objectives • Explain the relationship between force and energy. • Discriminate between contact forces and forces that act at a distance. • Identify common force units. • Compare the effect of balanced and unbalanced force on an object. • Apply the concept of net force to determine direction of motion. • Calculate net force

Standards: • SC. 6. P. 13. 1 Investigate and describe types of forces including contact forces and forces acting at a distance, such as electrical, magnetic, and gravitational. • SC. 6. P. 13. 3 Investigate and describe that an unbalanced force acting on an object changes its speed, or direction of motion, or both.

What is Force? • A force is simply a PUSH OR PULL. • Force is a vector quantity. All forces have both DIRECTION and SPEED (magnitude). • Scientists express force using an SI unit called the Newton (=1 kg·m/s 2) F=ma = mass x acceleration • International Systems of Unit (SI) = also known as the Metric System – the most widely used system of measurement ( made by the French) – Force = also measured pounds (lbs, oz) (made by English)

What is Force? • A force is simply a PUSH OR PULL. • Force is a vector quantity. All forces have both DIRECTION and SPEED (magnitude). • Scientists express force using an SI unit called the Newton (=1 kg·m/s 2) F=ma • Force can transmit energy to and from a body • It can transfer it through direct contact or at a distance

What are the different types of forces? • Contact Forces – Push/Pull – Friction • Non-Contact Forces – Electrical Energy – Magnetic Energy – Gravitational

• Friction – is a force that opposes(goes against) motion between two surfaces that are in contact. – EX) Friction is the reason your car stops when your parents slam on the brakes. Or lack of friction is when you slip on the ground • Normal Force – is the support force exerted upon an object that is in contact with another stable object – Is always perpendicular to the surface of contact

Balances and Forces • Balanced Forces • The net (total) force acting on any object is the combination of all the forces acting on that object • When the net force is zero (equal but opposite), the forces are balanced. • Balanced forces do not change the motion of an object

Balances and Forces • Unbalanced Forces • When the net force is not zero (equal but opposite), the forces are unbalanced. • Unbalanced forces will cause an object to accelerate(move) in the direction of the net force.

EXIT TICKET #1. • What is the unit of force in the metric system? A. joule B. kilogram C. newton D. pound

EXIT TICKET #2 • Which of these is evidence that an unbalanced force is acting on an object? A. The mass of the object is changing. B. The object remains at rest. C. The motion of the object is changing. D. The object continues moving in a straight line at constant velocity.

Standards: • SC. 6. P. 13. 1 Investigate and describe types of forces including contact forces and forces acting at a distance, such as electrical, magnetic, and gravitational. • SC. 6. P. 13. 3 Investigate and describe that an unbalanced force acting on an object changes its speed, or direction of motion, or both.

Objectives • Explain the relationship between force and energy. • Discriminate between contact forces and forces that act at a distance. • Identify common force units. • Compare the effect of balanced and unbalanced force on an object. • Apply the concept of net force to determine direction of motion. • Calculate net force

Contact Forces • Forces can transfer energy through direct contact – Applied Force (Fapp) -push or pull on an object changes its speed and/or direction of its motion.

Contact Forces • Forces can transfer energy through direct contact – Normal Force (Fnorm) -is the support force exerted upon an object that is in contact with another stable object

Contact Forces • Forces can transfer energy through direct contact – Frictional Force (Ffrict) the force exerted (used) by a surface as an object moves across it or makes an effort to move across it. – Two types – sliding(moving) & static (not moving) friction.

Contact Forces • Forces can transfer energy through direct contact – Tension Force (Ftens) force that is transmitted (pass on) through a string, rope, cable or wire when it is pulled tight on both ends

Contact Forces • Forces can transfer energy through direct contact – Spring Force (Fspring) force that is exerted (used) by a compressed (squished) or stretched spring.

Contact Forces • Forces can transfer energy through direct contact – Air Resistance(Fair) special type of frictional force (also known as Drag that acts upon objects as they travel through the air.

Non-Contact Forces • Electrostatic (Coulomb) Force (Felect ) – is the attraction (move towards) or repulsion ( move away from) of objects because of their electric charge. – Electrical energy is a flow or movement of electrically charged particles. – When combined with magnetic forces, electromagnets create strong forces that act over a distance.

Non-Contact Forces • MAGNETIC FORCE (Fmag) – attraction or repulsion that happens between electrically charged particles because of their motion. – The particle’s magnetic field exerts a force on another particle

Non-Contact Forces • MAGNETIC FORCE (Fmag) – can act on substances made of iron, nickel and cobalt from a distance. – Magnets have a north and south pole. Magnets can attract (opposite poles) or repel (same pole).

Non-Contact Forces • GRAVITATIONAL (Weight) FORCE (Fgrav) happens when two or more objects with mass pull on each other. – Larger Mass, Larger Gravity – Closer Together, Larger Gravity • Gravity pulls objects down towards the ground, even on an incline.

Non-Contact Forces • GRAVITATIONAL (Weight) FORCE- Fgrav – All objects upon earth experience a force of gravity that is directed "downward" towards the center of the earth. The force of gravity on earth is always equal to the weight of the object as found by the equation: – Fgrav = m * g – where g = 9. 8 N/kg (on Earth) – and m = mass (in kg)

Summary of Forces • https: //www. youtube. com/watch? v=v-BPYONLhl 8

EXIT TICKET #1 Paula pushes a skateboard and it gradually slows down to a stop. Why does the skateboard come to a stop? A. Gravity alone stops the skateboard. B. Paula did not push the skateboard with enough force. C. The skateboard has positive acceleration. D. Friction and gravity slow the skateboard.

EXIT TICKET #2 • How can some forces act at a distance without contact?

Objectives • Define inertia • Explain how the interaction of force pairs affects the motion of objects • Explain Newton’s three Laws of Motion

Newton’s Laws of Motion • Isaac Newton developed three laws that, together explain how and why objects move they way they do. – Law of Inertia – Acceleration – Action/Reaction

How do forces act on objects? • In the 1680 s, a British scientist named Sir Isaac Newton explained the relationship between force and motion with three laws of motion

Newton’s First Law • Law of Inertia – The tendency of an object to resist change in its motion. – An object that is at rest ( not moving) will remain at rest and an object that is in motion will remain moving at a constant velocity unless and until it experiences an unbalanced force. – Most common forces to influence a moving object is gravity and friction

Forces can start objects moving • An object will not start moving until a push or a pull is exerted upon it • Ex: A chair won’t slide across the floor unless a force pushes the chair

Forces Can Bring Objects to Rest • Objects will continue to move forever with the same velocity unless an unbalanced force acts on them • Ex: A car comes to a stop when the brakes are applied. (Friction from the road would also slow it down)

Newton’s Second Law • Acceleration- the acceleration of an object produced by the net force of all outside forces will be directly proportional (equal) to the magnitude of the force • It will be inversely (reverse) proportional to the mass of an object – The greater the mass for a given force the smaller the acceleration – The smaller the mass for a given force the larger the acceleration

Forces can accelerate objects • Ex: Grocery cart – When the cart is empty, it has less mass. Your force accelerates the cart quickly. But when it’s full, the same push accelerates the cart much more slowly

Newton’s Third Law • Law of Action and Reaction – When ever an object exerts a force on a second object, the second object exerts a force back that is equal and opposite in direction. – Force always happens in pairs – Happens at the same time but never on the same object – Forces are not always balanced – Ex. If one object has a greater mass it will cause the smaller object to accelerate from its force

How do force pairs act? • Third Law of Motion

Newton’s Laws of motion review • You. Tube Newton’s Laws of Motion in Sports • https: //www. youtube. com/watch? v=MAm 6 LOUn. J 80 • You. Tube Make. Me Genius Newton’s Three Laws of Motion • https: //www. youtube. com/watch? v=mn 34 mnn. Dn. KU

Standards: • SC. 6. P. 13. 1 Investigate and describe types of forces including contact forces and forces acting at a distance, such as electrical, magnetic, and gravitational. • SC. 6. P. 13. 3 Investigate and describe that an unbalanced force acting on an object changes its speed, or direction of motion, or both. • SC. 6. P. 12. 1 Measure and graph distance versus time for an object moving at a constant speed. Interpret this relationship.

Combinations of Forces • Not all forces cause an object to move. For example you are all sitting on chairs, this exerts a force. The chair exerts a force back to hold you up. This is a BALANCED FORCE.

How do multiple forces interact? • The net force is the combination of al the forces acting on an object • When forces act in the same direction, they are simply added together to determine the net force • When forces act in opposite directions, the smaller force is subtracted from the larger force

Balanced forces do not change motion • Net force of 0 N = BALANCED • Balanced forces will not cause a change in the motion of a moving object and will not cause a nonmoving object to start moving • Ex: Light hanging from ceiling

Unbalanced forces combine to produce acceleration • Net force is not 0 N, UNBALANCED • Unbalanced forces produce a change in motion, such as a change in speed or direction • This change in motion is acceleration

Net Force is a combination of forces • The net force will be in a direction that is a combination of the directions of the individual forces • When the forces are not of equal strength, the direction will be closer to the direction of the stronger force

• If forces on an object are not balanced, the object will be in motion until they are balanced again.

EXIT TICKET #1 Some forces require direct contact, while others, like gravity, act at a distance. Which of the following is NOT influenced by gravity? A. Earth's tides B. Your weight C. Earth's orbit D. Magnetism

EXIT TICKET #2 Gravity is a force that every mass exerts on every other mass. When you jump up in the air, not only does the Earth exert a gravitational force on you, but you also exert a gravitational force on the Earth. You, of course, fall back down to the Earth. Which of the following explains why the Earth is not moving toward you when you jump up in the air? A. Earth exerts a gravitational force on itself. B. You don't weigh enough to affect Earth's surface. C. Your mass is very small compared to Earth's mass. D. Earth's fixed orbit around the Sun keeps it from moving.

Exit Ticket # 3 Luis rubbed a balloon on his hair and held the balloon next to the wall. He observed the balloon stick to the wall. Which of the following is responsible for the balloon sticking to the wall? a) b) c) d) friction gravity electric force (static) magnetic force

Exit Ticket #4 The diagram below shows forces acting on a model airplane. Both its speed and height above the ground are constant. Which of the following conditions would cause the model airplane to descend toward the ground? a) The lift is equal to the drag. b) The lift is less than the weight. c) The thrust is equal to the weight. d) The thrust is greater than the drag.

Exit Ticket # 5