Chapter 10 Section 3-4 Newtons Laws of Motion
Chapter 10 Section 3-4 Newton’s Laws of Motion 7th Grade
Newton’s First Law of Motion • Scientists used to believe that the natural state of an object on the Earth was to be at rest. • They also believed that objects in motion on Earth required a force to keep them in motion. • Sir Isaac Newton shoed this was not true.
Newton’s First Law of Motion • Newton’s First Law states that an object will keep doing what it is doing (staying still, moving) if the forces acting on it are balanced (equal and opposite). • This means that an object that moves at a constant speed and in a straight line will continue that motion unless the forces acting on it are unbalanced.
Newton’s First Law of Motion • Because an object’s resistance to a change in its motion is called inertia, Newton’s first law of motion is also called the law of inertia. • As object’s mass is a measure of its inertia: the more mass an object has, the greater its inertia.
Newton’s First Law of Motion • Once an object is in motion, it stays in motion until it is acted on by another force. • When you roll a ball, it is slowed by friction and will eventually stop.
Describing Motion • Motion can be described by position, speed, direction, acceleration, etc. • When an object’s speed or direction changes, the object undergoes acceleration.
Describing Motion • Acceleration to most people mean increasing speed. • However, acceleration to scientists means any change in either the speed or the direction of an object’s motion. • So it is defined as the amount of change in speed per unit of time. Usually meters per second squared m/s2.
Describing Motion • So what causes an object to accelerate? • Force! • Remember a force is a push or pull that can cause the motion of an object to change.
Describing Motion • A contact force must touch an object to change its speed or direction. • Ex. When a bat hits a ball • Friction is another example of contact force. • Friction slows down objects due to particles of two materials catching on each other.
Describing Motion • Normal force is the force exerted by an object to balance an outside force acting on it. • Ex. When you sit in a chair, the chair exerts normal force on your body that is equal to the force of gravity pulling your mass toward the Earth.
Describing Motion • Non contact forces can act on objects from a distance. • Ex. Gravity, magnetism, and electricity
Newton’s Second Law of Motion • Newton’s Second Law of Motion states the acceleration of an object is related to the net force acting on it and to the object’s mass. • Force = mass x acceleration • Or • F = ma • The unit for force is Kg-m/s2 Or N (Newtons)
Newton’s Second Law of Motion • The net force on a 50 kg crate is 0 N. What is the acceleration? • F = ma • 0 N = (50 kg) a • 0 m/s2 = a
Newton’s Second Law of Motion • Scientists draw pictures called force diagrams to help them understand all of the forces acting on an object. • Remember force has a size and direction
Newton’s Second Law of Motion • Look at the table. In the first example, a 10 N force and a 20 N force pull an object to the right. The net force on the object is 30 N to the right. If the applied forces are … 10 N
…then the net force is: 30 N
20 N 10 N
15 N 25 N
Newton’s Second Law of Motion • In the second example, a 10 N force pulls an object to the left and a 25 N force pulls the object to the right. The net force on the object is 15 N to the right.
Newton’s Second Law of Motion • A force diagram does not show an object’s motion. The arrows show the size and direction of the forces acting on an object, not the speed or direction of the object itself.
Newton’s Third Law of Motion • Newton’s Third Law of Motion states that forces come in pairs: For every action, there is a reaction that is equal in magnitude (size) but opposite in direction.
Newton’s Third Law of Motion • Ex. Action force: hammer to nail • Reaction force: nail to hammer • Imagine a hammer pounding a nail into a board. The hammer supplies an action force, one that pushes the nail toward the left. The nail supplies a reaction force, one that is equal to the action force and pushes on the hammer toward the right.
Newton’s Third Law of Motion • Because the hammer is more massive than the nail, the nail moves away from the point of contact, into the wood. However, the same amount of force works on the hammer by stopping it; there might even be a slight rebound as the hammer moves away from the point of contact. That is the reaction force that the nail exerts on the hammer.
Review of the Laws • Now lets review the three laws!
Newton’s Second Law of Motion • Also known as the Law of Acceleration • Newton's Second Law of Motion states that when a force acts on an object, it will cause the object to accelerate. The larger the mass of the object, the greater the force will need to be to cause it to accelerate. This Law may be written as force = mass x acceleration • or:F = m * a
Newton’s Second Law of Motion • Another way to state the Second Law is to say it takes more force to move a heavy object than it does to move a light object.
Newton’s Third Law of Motion • Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. What this means is that pushing on an object causes that object to push back against you, the exact same amount, but in the opposite direction.
Newton’s Laws of Motion • Questions?
Newton’s First Law of Motion • Scientists used to believe that the natural state of an object on the Earth was to be at rest. • They also believed that objects in motion on Earth required a force to keep them in motion. • Sir Isaac Newton shoed this was not true.
Newton’s First Law of Motion • Newton’s First Law states that an object will keep doing what it is doing (staying still, moving) if the forces acting on it are balanced (equal and opposite). • This means that an object that moves at a constant speed and in a straight line will continue that motion unless the forces acting on it are unbalanced.
Newton’s First Law of Motion • Because an object’s resistance to a change in its motion is called inertia, Newton’s first law of motion is also called the law of inertia. • As object’s mass is a measure of its inertia: the more mass an object has, the greater its inertia.
Newton’s First Law of Motion • Once an object is in motion, it stays in motion until it is acted on by another force. • When you roll a ball, it is slowed by friction and will eventually stop.
Describing Motion • Motion can be described by position, speed, direction, acceleration, etc. • When an object’s speed or direction changes, the object undergoes acceleration.
Describing Motion • Acceleration to most people mean increasing speed. • However, acceleration to scientists means any change in either the speed or the direction of an object’s motion. • So it is defined as the amount of change in speed per unit of time. Usually meters per second squared m/s2.
Describing Motion • So what causes an object to accelerate? • Force! • Remember a force is a push or pull that can cause the motion of an object to change.
Describing Motion • A contact force must touch an object to change its speed or direction. • Ex. When a bat hits a ball • Friction is another example of contact force. • Friction slows down objects due to particles of two materials catching on each other.
Describing Motion • Normal force is the force exerted by an object to balance an outside force acting on it. • Ex. When you sit in a chair, the chair exerts normal force on your body that is equal to the force of gravity pulling your mass toward the Earth.
Describing Motion • Non contact forces can act on objects from a distance. • Ex. Gravity, magnetism, and electricity
Newton’s Second Law of Motion • Newton’s Second Law of Motion states the acceleration of an object is related to the net force acting on it and to the object’s mass. • Force = mass x acceleration • Or • F = ma • The unit for force is Kg-m/s2 Or N (Newtons)
Newton’s Second Law of Motion • The net force on a 50 kg crate is 0 N. What is the acceleration? • F = ma • 0 N = (50 kg) a • 0 m/s2 = a
Newton’s Second Law of Motion • Scientists draw pictures called force diagrams to help them understand all of the forces acting on an object. • Remember force has a size and direction
Newton’s Second Law of Motion • Look at the table. In the first example, a 10 N force and a 20 N force pull an object to the right. The net force on the object is 30 N to the right. If the applied forces are … 10 N
…then the net force is: 30 N
20 N 10 N
15 N 25 N
Newton’s Second Law of Motion • In the second example, a 10 N force pulls an object to the left and a 25 N force pulls the object to the right. The net force on the object is 15 N to the right.
Newton’s Second Law of Motion • A force diagram does not show an object’s motion. The arrows show the size and direction of the forces acting on an object, not the speed or direction of the object itself.
Newton’s Third Law of Motion • Newton’s Third Law of Motion states that forces come in pairs: For every action, there is a reaction that is equal in magnitude (size) but opposite in direction.
Newton’s Third Law of Motion • Ex. Action force: hammer to nail • Reaction force: nail to hammer • Imagine a hammer pounding a nail into a board. The hammer supplies an action force, one that pushes the nail toward the left. The nail supplies a reaction force, one that is equal to the action force and pushes on the hammer toward the right.
Newton’s Third Law of Motion • Because the hammer is more massive than the nail, the nail moves away from the point of contact, into the wood. However, the same amount of force works on the hammer by stopping it; there might even be a slight rebound as the hammer moves away from the point of contact. That is the reaction force that the nail exerts on the hammer.
Review of the Laws • Now lets review the three laws!
Newton’s Second Law of Motion • Also known as the Law of Acceleration • Newton's Second Law of Motion states that when a force acts on an object, it will cause the object to accelerate. The larger the mass of the object, the greater the force will need to be to cause it to accelerate. This Law may be written as force = mass x acceleration • or:F = m * a
Newton’s Second Law of Motion • Another way to state the Second Law is to say it takes more force to move a heavy object than it does to move a light object.
Newton’s Third Law of Motion • Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. What this means is that pushing on an object causes that object to push back against you, the exact same amount, but in the opposite direction.
Newton’s Laws of Motion • Questions?
