![]() ![]() It's any change in velocity, including speedups, slowdowns, and turns. TIM: In physics, acceleration isn't just speeding up. Tim and Moby, sitting in sideways placed seats, lean toward the back of the plane as it accelerates. The pilot looks back at Tim and Moby and pulls a lever up. TIM: We're gonna need to accelerate if this hunk of junk is gonna get off the ground. TIM: So, the net force on the plane is zero, same as if we weren't moving at all.Īs the plane taxis down the runway, an equal sign is placed between the arrow representing engine forces and the arrows representing drag and friction. And we're heading in a straight line.Ī split animation shows the plane's dial reading a steady 40 and an overhead view of the plane taxiing on a runway. The combination of these two values is called velocity. TIM: Well, we'd see a change in the plane's speed or direction. TIM: But notice how still it feels in here? If the forces were out of balance, we'd feel the push. After all, we're moving forward.Ī greater than sign is placed between the thick arrow representing the engine's force, and the two smaller arrows representing friction and drag. TIM: Yeah, you would think the force of the engines must be greater than friction and drag. TIM: And drag, which is basically the friction of air molecules.Ī thin red arrow points above the plane in the opposite direction of the plane's movement. TIM: There's friction, the resistance a surface puts on anything sliding over it.Ī thin red arrow points to the wheel in the opposite direction of the plane's movement. The engines are pulling the plane forward.Ī thick green arrow points in the direction the plane is moving. TIM: Right now, there are three main forces accounting for our movement. TIM: You're just trying to distract me, but fine. Tim and Moby appear inside the plane wearing skydiving gear. Moby then walks Tim to an old propeller plane that has a robot pilot. ![]() The dial measures 100 on Moby's side and his arrow reads 200N versus Tim's 100N. Aaack! That's any push or pull where the net force is not zero. TIM: To get me in motion, you'd need to exert an unbalanced force on me. TIM: It's named after Isaac Newton, the physicist who figured a lot of this stuff out. That's the unit we use to measure force.īoth Moby and Tim's arrows are labeled "100 N" and "Newtons" appears on the dial. The sum of the forces, or net force, is zero.Ī dial appears above the arrows and points to zero. Our forces are in balance, canceling each other out. TIM: Like right now we are pushing equally hard, in opposite directions. The arrows are different colors, red under Tim, green under Moby. Put in fancy science terms, we say force is a vector quantity.Īrrows point toward each other below Tim and Moby. Each one has a magnitude, the size of the force, and a direction. Objects usually have lots of forces acting on them at the same time. TIM: Well, it's never really that simple. Moby is trying to push a resisting Tim toward an airplane hangar. Something providing the push or pull, like Moby. And it always involves two or more objects. TIM: At its most basic, a force is a push or a pull. Like any time an object changes speed or direction.Ī split animation shows a skydiving man pulling his parachute cord and an overhead view of a plane making a turn on a runway. We can't see them, but some of their effects are pretty obvious. TIM: Forces are at work all the time, acting on everything around us. TIM: Dear Tim and Moby, If forces are invisible, how do we know they exist? And how do they work? Thanks, Katelin C. TIM: I, think I might just answer this letter. Tim sees they are at the X-Treme Rush Skydiving Center. TIM: You're the best robot pal a kid could ever– TIM: Man, I can't wait to see what my birthday activity is this year. Text reads: The Mysteries of Life with Tim and MobyĪ robot, Moby, leads a blindfolded boy, Tim, to an airport runway. ![]()
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