Newton's 1st Law & Forces
Look around and find something that's moving. Why is it moving? Just for fun? Now look at something that's not moving. Why is it not moving? Because it doesn't feel like it? Now that we've learned about how things move in kinematics, we can learn about why things move (or don't move).
This is the part of physics where things get a little more interesting. Things are happening all around you and you probably never gave a second thought about why they happen. As we start to learn about what's really going on, some things will be much more complex than you imagine, and some things will be way simpler.
We can see motion, but we can't really see the forces affecting that motion. If you roll a ball across the ground, you know it's going to slow down and stop because that's what things do. If you drop a pen, you know it's going to fall down and hit the floor because that's what things do. If you place a book on a table, you know it's not going to move because that's what things do.
But as we learn more about physics, try to set aside your intuitions about "what things do". We're going to build new intuitions about why things happen, intuitions that are based on the fundamentals of physics. Then we can understand anything in the universe, not just rolling balls and falling pens.
This lesson will start us off by introducing Newton's 1st law of Motion. This will help us understand how the forces acting on an object determine that object's motion (or lack of motion).
Things start to get a little complicated when we have many forces acting on an object, especially if the object is moving. That's where free body diagrams come in. A free body diagram (FBD) (also known as a force diagram) is a picture that isolates a single object (or a system) and shows all of the forces acting on that object. Forces are vectors so we represent them in the free body diagram with arrows that show their direction. Even if we think we know what's going on with an object, it's not until we actually draw a free body diagram and list each force that we can know for sure.
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Kinematics vs dynamics
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Why do objects move in different ways?
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Forces
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Different types of forces
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Free body diagrams
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Summary
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Try to explain 6 different examples of motion
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Net force, balanced and unbalanced forces
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Newton's 1st law of motion
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Using Newton's 1st law to explain the 6 examples of motion
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Summary
Answers
Free-Response Questions
Forces
- 2024 Q1 - - Block sliding on a track with loops, forces, FBDs, circular motion, energy
- 2024 Q3 - - Beam attached to a wall with a string, forces, FBDs, tension, rotational motion, torque
- 2024 Q5 - - Collision of two blocks, momentum, energy, forces
- 2022 Q1 - - Pulley system with 2 blocks and a spring, kinematics, forces, energy, work
- 2019 Q1 - - Plunger pushes block and sphere across surface, kinematics, forces, energy, work, torque, angular momentum
- 2019 Q2 - - Pulley system with 2 blocks, kinematics, forces, FBDs, tension, rotational motion
- 2018 Q1 - - Spacecraft in circular orbit, circular motion, forces, FBDs, law of gravitation
- 2017 Q2 - - (Experimental design) Coefficient of friction between block and board, forces, friction
- 2016 Q1 - - Wheel rolls down an incline, forces, FBDs, energy, friction
- 2015 Q1 - - Pulley system with 2 hanging blocks, forces, FBDs, tension
Free body diagrams
- 2024 Q1 - - Block sliding on a track with loops, forces, FBDs, circular motion, energy
- 2024 Q3 - - Beam attached to a wall with a string, forces, FBDs, tension, rotational motion, torque
- 2023 Q3 - - Block and spring rotating about axle, circular motion, centripetal force, FBDs
- 2022 Q2 - - Gravitational force between planet and moons, law of gravitation, FBD's
- 2019 Q2 - - Pulley system with 2 blocks, kinematics, forces, FBDs, tension, rotational motion
- 2018 Q1 - - Spacecraft in circular orbit, circular motion, forces, FBDs, law of gravitation
- 2016 Q1 - - Wheel rolls down an incline, forces, FBDs, energy, friction
- 2015 Q1 - - Pulley system with 2 hanging blocks, forces, FBDs, tension
- 2015 Q4 - - Projectile motion of two spheres, projectile motion, FBDs
- Newton's 1st Law of Motion
- Khan Academy - Newton's first law of motion
- Khan Academy - More on Newton's first law of motion
- Khan Academy - Balanced and unbalanced forces
- Free body diagrams
Look around and find something that's moving. Why is it moving? Just for fun? Now look at something that's not moving. Why is it not moving? Because it doesn't feel like it? Now that we've learned about how things move in kinematics, we can learn about why things move (or don't move).
This is the part of physics where things get a little more interesting. Things are happening all around you and you probably never gave a second thought about why they happen. As we start to learn about what's really going on, some things will be much more complex than you imagine, and some things will be way simpler.
We can see motion, but we can't really see the forces affecting that motion. If you roll a ball across the ground, you know it's going to slow down and stop because that's what things do. If you drop a pen, you know it's going to fall down and hit the floor because that's what things do. If you place a book on a table, you know it's not going to move because that's what things do.
But as we learn more about physics, try to set aside your intuitions about "what things do". We're going to build new intuitions about why things happen, intuitions that are based on the fundamentals of physics. Then we can understand anything in the universe, not just rolling balls and falling pens.
This lesson will start us off by introducing Newton's 1st law of Motion. This will help us understand how the forces acting on an object determine that object's motion (or lack of motion).
Things start to get a little complicated when we have many forces acting on an object, especially if the object is moving. That's where free body diagrams come in. A free body diagram (FBD) (also known as a force diagram) is a picture that isolates a single object (or a system) and shows all of the forces acting on that object. Forces are vectors so we represent them in the free body diagram with arrows that show their direction. Even if we think we know what's going on with an object, it's not until we actually draw a free body diagram and list each force that we can know for sure.
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