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Fun Science Facts for Kids All about The first Law of Motion – Sir Isaac Newton Fun Facts. The first law of motion states that: an object at rest will stay at rest. An object in motion stays in motion unless acted upon by an unbalanced force. Your soccer ball won’t move unless you kick it.
- Overview
- Why do objects slow down?
- What do force, external force, and net force mean?
- What does mass mean?
- Example 1: space probe drift
- Example 2: elevator lift
- Example 3: space probe path
Also called the law of inertia, this is the most important thing to realize about motion.
Why do objects slow down?
Before Galileo and Newton, many people thought objects slowed down because they had a natural built in tendency to do so. But those people weren't taking into account the many forces—e.g., friction, gravity, and air resistance—here on Earth that cause objects to change their velocity. If we could observe the motion of an object in deep interstellar space, we would be able to observe the natural tendencies of an object's motion free from any external influences. In deep interstellar space, we would observe that if an object had a velocity, it would continue moving with that velocity until there was some force to cause a change in the motion. Similarly, if an object were at rest in interstellar space, it would remain at rest until there was a force to cause it to change its motion.
In the video below, we can see that objects in the international space station either remain at rest or continue with constant velocity relative to the space station until acted upon by a force.
[Wait, isn't there still gravity at the space station?]
Khan Academy video wrapper
Before Galileo and Newton, many people thought objects slowed down because they had a natural built in tendency to do so. But those people weren't taking into account the many forces—e.g., friction, gravity, and air resistance—here on Earth that cause objects to change their velocity. If we could observe the motion of an object in deep interstellar space, we would be able to observe the natural tendencies of an object's motion free from any external influences. In deep interstellar space, we would observe that if an object had a velocity, it would continue moving with that velocity until there was some force to cause a change in the motion. Similarly, if an object were at rest in interstellar space, it would remain at rest until there was a force to cause it to change its motion.
In the video below, we can see that objects in the international space station either remain at rest or continue with constant velocity relative to the space station until acted upon by a force.
[Wait, isn't there still gravity at the space station?]
Khan Academy video wrapper
See video transcript
The idea that objects only change their velocity due to a force is encapsulated in Newton's first law.
A force is a push or a pull exerted on one object by another object. The units of force F are called Newtons or simply N .
An external force is a force originating from outside an object rather than a force internal to an object. For instance, the force of gravity that Earth exerts on the moon is an external force on the moon. However, the force of gravity that the inner core of the moon exerts on the outer crust of the moon is an internal force on the moon. Internal forces within an object can't cause a change in that object's overall motion.
The net force, written as ΣF , on an object is the total force on an object. If many forces act on an object, then the net force is the sum of all the forces. But be careful—since force F is a vector, to find the net force ΣF , the forces must be added up like vectors using vector addition.
In other words, if a box of frozen burritos had a force of magnitude 45 Newtons exerted on it to the right and a force of magnitude 30 Newtons exerted on it to the left, the net force in the horizontal direction would be
ΣFhorizontal=45 N−30 N
ΣFhorizontal=15 N
The property of a body to remain at rest or to remain in motion with constant velocity is called inertia. Newton’s first law is often called the law of inertia. As we know from experience, some objects have more inertia than others. It is obviously more difficult to change the motion of a large boulder than that of a basketball, for example.
The inertia of an object is measured by its mass. Mass can be determined by measuring how difficult an object is to accelerate. The more mass an object has, the harder it is to accelerate.
A space probe is drifting to the right at a constant velocity in deep interstellar space—far from any influence due to planets and stars—with its rockets off. If two rocket thrusters both turn on simultaneously exerting identical forces leftward and rightward in the directions shown, what would happen to the motion of the rocket?
a. The space probe would continue with constant velocity.
b. The space probe would speed up.
c. The space probe would slow down and eventually stop.
d. The space probe would immediately stop.
The correct answer is a. According to Newton's first law, a non-zero net force is required to change the velocity of an object. The net force on the space probe is zero—since the forces on it cancel—so there is no change in the velocity of the probe.
An elevator is being pulled upward at a constant velocity by a cable as seen in the diagram below. While the elevator is moving upward at constant velocity, how does the magnitude of the upward force exerted on the elevator by the cable—Fc —compare to the magnitude of the downward force of gravity—Fg —on the elevator?
a. Fc is greater than Fg .
b. Fc is equal to Fg .
c. Fc is smaller than Fg .
d. Fc could be larger or smaller than Fg depending on the mass of the elevator.
The correct answer is b. If the elevator is moving with constant velocity, the net force must be zero. In order for the net force on the elevator to be zero, the upward and downward forces must cancel exactly.
A space probe is drifting to the right with constant velocity in deep interstellar space—far from any influence due to planets and stars. If a rocket thruster turns on and then off for a short burst of force in the direction shown, what would best represent the path traveled by the rocket after the thruster turns off?
a. Path a
b. Path b
c. Path c
d. Path d
The correct answer is c. After the rocket thruster turns off, there will be no net force on the space probe. Once the net force is zero, the velocity—both magnitude and direction—must be constant. Because of Newton's first law, the space probe moves in a straight line at constant speed. The fact that there was a vertical force on the space probe does not affect the horizontal velocity of the space probe, it only changes the vertical velocity. A constant vertical and horizontal velocity yields a diagonal straight line through space.
16 de feb. de 2021 · Newton’s First Law. Imagine you want to play soccer with your friends. To win or even start the game, one of your teammates has to kick the ball — otherwise, the ball won’t move by itself. This is what the 1st Low implies: Unless you push or pull (apply a force on) an object, it will remain at rest or in uniform.
A scientist named Isaac Newton came up with three Laws of Motion to describe how things move scientifically. He also described how gravity works, which is an important force that affects everything. First Law of Motion. The first law says that any object in motion will continue to move in the same direction and speed unless forces act on it.
16 de oct. de 2023 · Isaac Newton (1642–1727), the father of the study of dynamics – the study of motion – developed three sets of laws that are believed to be true because the results of tests done by scientists agree with the laws he produced. Contents. First law. Second law. Third law. Related pages. Images for kids. See also. First law.
First Law. The first law says that an object at rest tends to stay at rest, and an object in motion tends to stay in motion, with the same direction and speed. Motion (or lack of motion) cannot change without an unbalanced force acting.
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