# FORCES Ch.10 “May the Force be with You”. I. Force All forces are exerted by one object on another object. All forces are exerted by one object on another.

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FORCES Ch.10 “May the Force be with You”

I. Force All forces are exerted by one object on another object. All forces are exerted by one object on another object. For any push to occur something has to receive the push. For any push to occur something has to receive the push.

Newton (N) Newton (N) The SI unit scientists use to measure force. The SI unit scientists use to measure force.

I. Force A force is: A push or a pull. A force is: A push or a pull. All forces have both size (magnitude) and direction. All forces have both size (magnitude) and direction. more Newtons = more force more Newtons = more force

Net Force Net Force Net Force is The force that results from combining all the forces exerted on an object. Net Force is The force that results from combining all the forces exerted on an object. The motion of an object will be determined by net force The motion of an object will be determined by net force

Net Force Net Force UNBALANCED FORCES - **net force is greater than zero **causes a change in the object’s velocity **causes a change in the object’s velocity(acceleration)

Net Force BALANCED FORCES ** the object’s motion does not change ** the object’s motion does not change **net forces equals zero

II. Friction A force that opposes motion between two surfaces that are touching. A force that opposes motion between two surfaces that are touching. Rougher surfaces create more friction. Rougher surfaces create more friction. Greater forces create more friction. Greater forces create more friction. Friction results in heat (objects that rub together, heat up) Friction results in heat (objects that rub together, heat up)

. Types of Friction 1. Static Friction 1. Static Friction 2. Sliding Friction 2. Sliding Friction 3. Fluid Friction 3. Fluid Friction 4. Rolling Friction 4. Rolling Friction

III. Gravity The force of attraction between objects that is due to their masses. The force of attraction between objects that is due to their masses. All matter has mass! All matter has mass! Therefore…??? Therefore…???

IV. Law of Universal Gravitation This law describes the relationship between gravitational force, mass, and distance. This law was worked out by Newton. This law describes the relationship between gravitational force, mass, and distance. This law was worked out by Newton.

IV. Law of Universal Gravitation 1. Gravitational force is small between objects with small masses. 1. Gravitational force is small between objects with small masses. 2. Gravitational force is large between objects with large masses. 2. Gravitational force is large between objects with large masses.

IV. Law of Universal Gravitation 3. The larger the distance between two objects, the smaller the gravitational force is between them. 3. The larger the distance between two objects, the smaller the gravitational force is between them.

V. Weight The measure of the gravitational force exerted on an object. The measure of the gravitational force exerted on an object. Weight is measured with a spring scale. Weight is measured with a spring scale. Weight = mass X acceleration Weight = mass X acceleration

VI. Mass The amount of matter in an object. The amount of matter in an object. Mass is measured with a balance. Mass is measured with a balance.

VII. Gravity & Motion 1. FREE FALL- acceleration of a falling object due to the pull of gravity only. 1. FREE FALL- acceleration of a falling object due to the pull of gravity only. 2. AIR RESISTANCE- fluid friction of air acting on an object falling through air 2. AIR RESISTANCE- fluid friction of air acting on an object falling through air

VII. Gravity & Motion 3. PROJECTILE MOTION - is motion of a thrown object. Two forces act on it. One is the force of the throwing motion (horizonal) and the other is the force of gravity (vertical) 3. PROJECTILE MOTION - is motion of a thrown object. Two forces act on it. One is the force of the throwing motion (horizonal) and the other is the force of gravity (vertical)

Orbiting objects Objects in orbit are in projectile motion

VIII. Elastic Forces Matter is elastic if it returns to its original shape after being squeezed or stretched Matter is elastic if it returns to its original shape after being squeezed or stretched Compression is the elastic force when an object is pushed together. Compression is the elastic force when an object is pushed together. Tension- is the elastic force that stretches or pulls an object Tension- is the elastic force that stretches or pulls an object

IX. Newton’s Laws Isaac Newton (1642-1727) described 3 important laws that help us understand forces. These laws seem simple and obvious to us and we tend to take them for granted. Almost every aspect of our lives involves one or more of them. Isaac Newton (1642-1727) described 3 important laws that help us understand forces. These laws seem simple and obvious to us and we tend to take them for granted. Almost every aspect of our lives involves one or more of them.

Newton’s 1 st Law of Motion: An object will remain at rest or moving at a constant velocity unless it is acted upon by an unbalanced force An object will remain at rest or moving at a constant velocity unless it is acted upon by an unbalanced force

Newton’s 1 st Law of Motion: “An object in motion will stay in motion, an object at rest will stay at rest unless acted upon by an outside force.” “An object in motion will stay in motion, an object at rest will stay at rest unless acted upon by an outside force.”

Newton’s 1 st Law of Motion: 1. An unbalanced force will cause an object to speed up, slow down or change direction 1. An unbalanced force will cause an object to speed up, slow down or change direction 2. Inertia is the tendency of an object to resist a change in motion 2. Inertia is the tendency of an object to resist a change in motion

Newton’s 1 st Law of Motion: 3. Inertia depends on the mass of an object. 3. Inertia depends on the mass of an object. The greater the mass, the greater the inertia and the greater the force required to change the motion. The greater the mass, the greater the inertia and the greater the force required to change the motion.

Newton’s 2 nd Law of Motion: Acceleration depends on the net force acting on the object and the object’s mass Acceleration depends on the net force acting on the object and the object’s mass

Newton’s 2 nd Law of Motion: “When a force is applied to an object, the object accelerates in the direction of the applied force. The acceleration is less when the mass of the object is greater.” “When a force is applied to an object, the object accelerates in the direction of the applied force. The acceleration is less when the mass of the object is greater.”

Newton’s 2 nd Law of Motion: Net force = mass Net force = massAcceleration OR net force = mass X acceleration OR net force = mass X acceleration ex: Think of kicking a football and a rock the size of a football. You would need a lot more force to move the rock the same distance as the football.

Newton’s 3 rd Law of Motion: If one object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction on the first object If one object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction on the first object

Newton’s 3 rd Law of Motion: “For every force (action) there is an equal and opposite force (reaction). If you push or pull on an object, the object will push or pull back with equal and opposite force.” “For every force (action) there is an equal and opposite force (reaction). If you push or pull on an object, the object will push or pull back with equal and opposite force.”

X. Momentum A. depends on mass and velocity A. depends on mass and velocity B. Momentum is described by size and direction B. Momentum is described by size and direction C. Momentum = mass X velocity C. Momentum = mass X velocity D. The more momentum an object has the harder it is to change it’s velocity D. The more momentum an object has the harder it is to change it’s velocity

XI. Conservation of Momentum the total momentum of a group of objects stays the same, or is conserved, unless outside forces act on the objects

XI. Conservation of Momentum A. Collisions of 2 moving objects – the momentum of one object decreases and the momentum of the other object will increase A. Collisions of 2 moving objects – the momentum of one object decreases and the momentum of the other object will increase B. Collision of 1 moving object (with a stationary object)– the momentum of the moving object is transferred to the other object B. Collision of 1 moving object (with a stationary object)– the momentum of the moving object is transferred to the other object

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