Forces and Motion
A ball sitting still on the floor suddenly starts rolling. What must have been exerted on it?
A force (push or a pull)
A marble rolls across a carpet and eventually stops. What force stopped it?
Friction
A bowling ball and a beach ball are the same size. Which one has more mass?
A bowling ball
When two objects collide, does a force act on one object or on both?
Both objects
In a scientific argument, what do we call the statement you are trying to prove?
A claim
Name any THREE of the five ways an object's motion can change.
Any three: start, stop, speed up, slow down, change direction
Compared to an object's motion, which direction does friction push?
Opposite to the direction of motion
You give an empty shopping cart and a full shopping cart the same push. Which one speeds up more?
The empty cart, because it has less mass.
A marble rolling to the right hits a marble that is standing still. Which direction is the force on the moving marble?
To the left, opposite to its motion.
What is reasoning?
Explaining how the evidence supports (or refutes) the claim.
A skateboarder is rolling forward. A friend pushes her from behind in the same direction. What happens to her velocity?
She speeds up, because the force is in the same direction as her motion.
The same toy car is pushed with the same force on ice and on carpet. Where does it roll farther, and why?
On ice, because there is less friction to slow it down.
A wheelchair basketball player wants to start, stop, and turn quickly. Should the chair have more or less mass? Why?
Less mass, because the same force will cause a greater change in velocity.
A fly hits the windshield of a moving bus. Compare the force on the fly to the force on the bus.
They are the same strength, but in opposite directions.
Which is stronger evidence that less mass means a bigger change in velocity: "My friend thinks so" or "In the Sim, the mass-1 object changed velocity 4 times more than the mass-4 object"? Why?
The Sim data, because it is specific, measured evidence.
A runner travels 300 meters in 60 seconds. What is her speed?
5 m/s (300 ÷ 60)
You tap a soccer ball gently, then kick it hard. Which causes the greater change in velocity, and why?
The hard kick, because a stronger force causes a greater change in velocity.
Object A has a mass of 2 and Object B has a mass of 1. The same force is exerted on both. Object B's velocity changes by 6 cm/s. How much does Object A's change?
3 cm/s, because A has twice the mass, so it changes half as much.
In that same crash, the fly gets squashed, but the bus barely changes speed. Why?
The fly has much less mass, so the same strength force causes a much greater change in velocity.
Kinetic energy depends on which two things about a moving object?
Its mass and its velocity (speed).
Two cars both drive at 50 km/h. One goes north and one goes south. Do they have the same speed? The same velocity? Explain.
Same speed, but different velocities, because velocity is speed in a particular direction.
Explain the whole story, from the thrusters firing to the pod moving away faster than the station.
The pod had extra mass, so the thruster force only slowed it down. It hit the station. Both felt equal and opposite forces. The pod has less mass than the station, so it had a greater change in velocity and moved away faster.
You want a heavy cart and a light cart to have the SAME change in velocity. What must you do differently, and why?
Exert a stronger force on the heavy cart, because more mass needs more force for the same change in velocity.
Object A (mass 4) and Object B (mass 1) collide. Object A's velocity changes by 2 cm/s. How much does Object B's velocity change? Explain.
8 cm/s. The forces are equal, and B has one-fourth the mass, so it changes four times as much.
A bike's speed triples. How many times more kinetic energy does it have?
9 times as much, because kinetic energy grows with the square of speed (3 × 3).