Newton's laws

TEKS: 8.3C

8.3 Scientific Investigation and Reasoning. The student uses critical thinking, scientific reasoning, and problem solving to make informed decisions and knows the contributions of relevant scientists. The student is expected to:

(D) relate the impact of research on scientific thought and society, including the history of science and contributions of scientists as related to the content.

TEKS: 8.6C8.6 Force, motion, and energy. The student knows

that there is a relationship between force, motion, and energy. The student is expected to:

(C) investigate and describe applications of Newton’s law of inertia, law of force and acceleration, and law of action-reaction such as in vehicle restraints, sports activities, amusement park rides, Earth’s tectonic activities*, and rocket launches.

*Will be covered in 3rd Six Weeks.

• One of the most influential scientists of all time• English physicist, mathematician, astronomer,

natural philosopher, alchemist, and theologian• Invented a reflecting telescope, which brought

him much fame and attention (1668)• Wrote Principia Mathematica, one of the most

influential science books in history (discusses universal gravitation and laws of motion) (1687)

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Also called the law of inertia.

• In other words an object will keep doing whatever it’s doing (still or moving) unless an unbalanced force acts on it.

• Example: Your skateboard will stay lying in the driveway until someone moves it. And, if your skateboard suddenly hits a curb and stops short… you will keep moving until something stops you!

• Newton’s 1st law is also known as the Law of Inertia.Inertia. (Inertia is an object’s (Inertia is an object’s tendency to resist a change in tendency to resist a change in motion.)motion.)

• The greater an object’s mass, the greater The greater an object’s mass, the greater its inertia, and the larger the force needed its inertia, and the larger the force needed to overcome the inertia.to overcome the inertia.

•Which vehicle would take longer to stop?•It will take longer for the dump truck to stop than the car, because the dump truck has more mass.

A property of matter

The tendency of an object to resist any change in its motion

The greater the mass the greater the inertia

The greater the speed the greater the inertia

All About Inertia

Examples of Newton’s 1st Law

• car suddenly stops and you strain against the seat belt because our bodies want to keep moving

• when riding a horse, the horse suddenly stops and you fly over its head • the difficulty of pushing a dead car

• car turns left and you appear to slide to the right

• ketchup stays in the bottom (at rest) until you bang (outside force) on the end of the bottom

• a headrest in a car prevents whiplash injuries during a rear-end collision (your head goes forward and then jerks backward)

Newtons’s 1st Law and You

Don’t let this be you. Wear seat belts.Don’t let this be you. Wear seat belts.

Because of inertia, objects (including you) Because of inertia, objects (including you) resist changes in their motion. When the resist changes in their motion. When the car going 80 km/hour is stopped by the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 brick wall, your body keeps moving at 80 m/hour.m/hour.

Newton’s 2nd Law

Force= mass x acceleration

Second law: The greater the force applied to an object, the more the object will accelerate. It takes more force to accelerate an object with a lot of mass than to accelerate something with very little mass. The player in black had more

acceleration thus he hit with a greater amount of force

Second law:The greater the force, the greater the

accelerationThe greater the mass, the greater the

force needed for the same accelerationCalculated by: F = ma(F = force, m = mass, a = acceleration)

Newton’s 2nd Law proves that different masses accelerate to the earth at the same rate, but with different forces.

• We know that objects with different masses accelerate to the ground at the same rate.

• However, because of the 2nd Law we know that they don’t hit the ground with the same force.

F = maF = ma

98 N = 10 kg x 9.8 m/s/s98 N = 10 kg x 9.8 m/s/s

F = maF = ma

9.8 N = 1 kg x 9.8 9.8 N = 1 kg x 9.8 m/s/sm/s/s

Examples of Newton’s 2nd Law

• hitting a baseball, the harder the hit, the faster the ball goes

• accelerating or decelerating a car

•The positioning of football players – massive players on the line with lighter (faster to accelerate) players in the backfield

• a loaded truck versus an unloaded truck

Newton’s 3rd Law

• For every action force, there is an equal and opposite reaction force. (Forces are always found in pairs.)

• Athlete pushes bar upwards.• Bar pushes the athlete downwards.

• Bowling ball pushes pin to the right.• Pin pushes bowling ball to the left.

Newton’s 3rd Law

3rd Law

Reaction of a rocket. Fuels Reaction of a rocket. Fuels are burned in the engine, are burned in the engine, producing hot gases. producing hot gases.

The hot gases push against The hot gases push against the inside tube of the rocket the inside tube of the rocket and escape out the bottom and escape out the bottom of the tube. As the gases of the tube. As the gases move downward, the rocket move downward, the rocket moves in the opposite moves in the opposite direction.direction.

Examples 3rd Law

•Momentum of the car moving forward and the car comes to a sudden stop, our body pushes against the seat (action) belt and the seat belt pushes back (reaction).

•When you lean on the wall to rest, the weight on the wall provides the reaction force and the wall pushes back on you (reaction force) with the same force.

• Roller coaster ride- The train to the tracks.•Birds wings to the air.

Car to the tracks- 3rd Law