The English scientist Isaac Newton, who lived around 1700, was curious about how forces affect the motion of objects. After a lot of study and observation, he was able to explain the relationship between forces and Motion.
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Inertia is the tendency of an object to resist a change in its motion. All objects have inertia, whether they are stationary or moving. Inertia explains Newton’s first law of motion, which states that an object at rest will remain at rest, and an object in motion will stay in motion unless it is acted on by an unbalanced force. Newton’s first law of motion is sometimes called the law of inertia.
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Consider what happens when you roll a ball across a floor. According to Newton’s first law, the ball should keep rolling until a force acts on it to make it stop rolling. What force makes the ball stop rolling? Friction is the resistance force that is created when the ball rubs on the ground. Friction is always in the opposite direction of motion. Friction is the force that makes the ball stop rolling.
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Any change in motion is known as acceleration. If there is no change in the motion of an object, meaning it is either at rest (not moving) or in motion at a continuous speed, then the forces acting on the object are balanced.
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In the picture below you can see the two children exerting a force on the ball to move it across the grass. If they do not push on it, it will not move.
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Newton observed a pattern in the relationship between force (a push or pull) and motion. He noticed that a force is needed to make a stationary object start moving. In other words, objects at rest stay at rest unless acted upon by an outside force. Newton also noticed that a moving object will only slow down, speed up, or change direction if an outside force pushes or pulls it. So, objects continue to do the same thing unless a force acts on them.
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The inertia of an object depends on its mass. Mass is the amount of matter in an object. Objects with greater mass also have greater inertia. The measurement of an object’s inertia while at rest is the object’s mass.
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Any time there is a change in the motion, like speeding up or slowing down, there is an unbalanced force.
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What was one key interest of Isaac Newton?
Human behavior
Chemical reactions
How forces affect motion
What action is needed to move an object that is not moving?
Applying a force
Waiting for it to move
Pushing or pulling the object
Sitting still beside it
When is a force required on a moving object?
To change its speed
To change its direction
To keep it moving at the same speed
It doesn’t need any force
Which action shows an example of force?
Standing next to the box
Pushing a box
Pulling a rope
Watching the box
What happens when no force acts on an object?
It keeps doing what it was doing
It starts moving faster
It stays in its current state
It stops moving altogether
According to Newton’s first law, what happens to an object at rest?
It will eventually start moving on its own
It stays at rest without a force
It speeds up until stopped
What is required for an object in motion to change its motion?
An unbalanced force
More mass must be added
No force is needed
Which bucket is more difficult to push?
The bucket with sand
The bucket with greater mass
The empty bucket
The bucket with less inertia
What does mass affect in an object?
Inertia
Its temperature
Its color
Why is the sand bucket harder to move?
It is smaller in size
It contains more mass
It is heavier in weight only
It has greater inertia
Which statement is true about mass and inertia?
Greater mass means greater inertia
Inertia depends on the mass of an object
Inertia is the same regardless of mass
Less mass means less inertia
What role does friction play when a ball rolls on the ground?
It makes the ball speed up
It slows down the ball
It does not affect the ball
In which direction does friction act on a rolling ball?
In the same direction as motion
Opposite to the motion
Downward towards the ground
What causes the ball to eventually stop rolling on the floor?
Gravity pulling it down
Air resistance pushing it forward
Friction with the ground
What happens when two people pull on a rope with different strengths?
The object experiences an unbalanced force
The object's motion changes
The forces are balanced
No motion occurs
Which of the following describes unbalanced forces?
They always slow down motion
They can change the direction of an object
They only act in one direction
Why is it important to understand unbalanced forces?
They are only relevant in space
They explain changes in an object's motion
They apply only to heavy objects
They help predict how objects will move
In the image, which action demonstrates an unbalanced force?
One person pulling harder than the other
Both people pulling equally
No force being applied
What indicates that forces on an object are balanced?
The object changes direction
The object speeds up
The object stays at rest
The object moves at a constant speed
What occurs when forces acting on an object are unbalanced?
The object remains stationary
The object accelerates
The object's motion changes
The object experiences no force
If a box is not moving, what can be concluded about the forces on it?
Forces are causing acceleration
Forces are acting unevenly
Forces are balanced
What causes the ball to move in the image?
The ball moving on its own
The children exerting force on it
The wind pushing it
Which of the following statements is true based on the image?