Forces in Action
A student pulls a wagon toward herself using the handle.
Identify the type of force being used and explain why it is a contact force.
The student is using a pull. It is a contact force because the student must physically touch the wagon handle for the force to act.
Two students push on opposite sides of a box with equal force. The box remains still.
Explain why the box does not move.
The forces are equal in strength and opposite in direction, so they are balanced. Balanced forces do not cause a change in motion.
A student pushes a stationary toy truck and the truck begins moving.
Explain how energy is transferred in this situation.
Energy is transferred from the student to the toy truck through the push, causing the truck’s motion to change.
A student wants to test how the amount of force applied to a toy car affects how far the car travels.
Identify the variable the student should change and the variable the student should measure.
The student should change the amount of force applied and measure the distance the car travels.
A toy car travels:
Describe the pattern shown by the results.
As the amount of force increases, the distance the car travels also increases.
A paper clip begins moving toward a magnet even though the magnet never touches it.
Identify the force causing the motion and explain how you know it acts at a distance.
Magnetic force causes the paper clip to move. It acts at a distance because the magnet changes the paper clip’s motion without touching it.
A toy car moves in a straight line at a constant speed.
What does this tell you about the forces acting on the car? Explain.
The forces are balanced because the car’s speed and direction are not changing.
A ball rolls across a rough carpet and gradually slows down.
Explain why the ball slows down.
Friction between the ball and the carpet acts against the ball’s motion, causing it to slow down.
A student tests whether surface type affects the distance a toy car travels. The student uses tile, carpet, and sandpaper.
Name two things the student should keep the same during every trial and explain why.
Possible constants include the same toy car, starting point, amount of force, and ramp setup. Keeping them the same makes the test fair so surface type is the main variable being tested.
A group tests a toy car three times under the same conditions.
What do these results suggest about the reliability of the investigation?
The results are very similar, suggesting the investigation produced consistent and reliable results.
A basketball falls from a shelf to the floor.
Explain which force causes the basketball to fall and whether that force requires contact.
Gravity pulls the basketball toward Earth. Gravity acts at a distance, so it does not require physical contact.
One student pushes a crate east with 16 N of force. Another student pushes west with 10 N of force.
Predict how the crate’s motion will change and justify your answer.
The crate will accelerate east because the eastward force is greater. The forces are unbalanced, with a net force of 6 N east.
Two identical toy cars are pushed across the same floor. Car A receives a gentle push. Car B receives a much stronger push.
Predict how the motion of the two cars will differ and explain why.
Car B should experience a greater change in motion, such as moving faster or farther, because a greater force was applied to it
A student tests how force affects a cart but changes both the amount of force and the mass of the cart during every trial.
Explain why the student cannot confidently determine what caused the changes in motion.
The student changed more than one variable. Changes in motion could have been caused by the amount of force, the mass of the cart, or both.
Students collect these results:
Force Distance
2 N 40 cm
4 N 79 cm
6 N 121 cm
Write a conclusion supported by evidence from the data.
Increasing the force caused the car to travel farther. At 2 N, the car traveled 40 cm, while at 6 N, it traveled 121 cm.
A student pushes a box across the floor while gravity also pulls downward on the box.
Compare the two forces acting on the box.
The student's push is a contact force because the student touches the box. Gravity is a noncontact force because it pulls the box toward Earth without direct contact.
A rolling cart is moving north. A strong force is suddenly applied toward the south.
Describe how the cart’s motion could change and explain why
The cart could slow down, stop, or begin moving south depending on the strength and duration of the southward force. The force is acting opposite the cart’s current motion.
A toy car travels 150 cm across tile but only 65 cm across thick carpet after receiving the same push.
Explain why the car travels different distances on the two surfaces.
The carpet creates more friction than the tile. Greater friction opposes the car’s motion more strongly, so the car slows sooner and travels a shorter distance.
A student wants to determine whether a stronger push makes a toy car move faster.
Design a fair investigation. Identify what should change, what should be measured, and two variables that should remain constant.
The student should change the amount of force and measure the car’s speed. The same car, surface, starting point, direction, or measuring procedure should remain constant.
A student collects the following results:
Trial Force Distance
1 3 N 58 cm
2 5 N 102 cm
3 7 N 61 cm
Identify the result that does not fit the overall pattern and explain what the student should do next.
Trial 3 does not fit the expected increasing pattern. The student should repeat the trial and check whether all variables were controlled and measurements were accurate.
A metal cart is pulled to the right with a string while a magnet attracts the cart toward the left.
Explain what determines which direction the cart’s motion will change.
The cart’s motion depends on the direction and strength of the forces. If one force is greater, the forces are unbalanced and the cart’s motion will change in the direction of the greater force.
A sled is moving forward while friction acts backward. The pulling force on the sled is greater than the friction force.
Explain whether the forces are balanced or unbalanced and predict what will happen to the sled’s motion.
The forces are unbalanced because the pulling force is greater than friction. The sled will accelerate forward.
A student says, “When friction stops a moving object, the object’s energy is destroyed.”
Evaluate the student’s statement and explain what actually happens.
The statement is incorrect. Energy is not destroyed. Friction transfers some of the moving object’s energy to the surroundings, often as thermal energy.
A student tests a toy car three times but starts the car from a different location and uses a different floor surface during each trial.
Evaluate the investigation and explain two changes that would make the results more reliable.
The investigation is not well controlled. The student should use the same starting point and the same floor surface during each trial so only the intended variable changes
One group conducts three trials and gets distances of 43 cm, 85 cm, and 128 cm as force increases. Another group gets 91 cm, 46 cm, and 119 cm as force increases.
Which group provides stronger evidence of a relationship between force and motion? Justify your answer.
The first group provides stronger evidence because the distance consistently increases as the amount of force increases. The second group’s results do not show a consistent pattern.