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Understand the TEKS

It is important to understand these terms as you learn about what makes an object move.

Inertia is a property of matter that causes it to resist changes in speed.

A force is a push or pull that can change an object’s motion.

Gravity is the force of attraction between objects. Gravity can also cause motion.

Friction is a force that occurs when two objects rub together.

Guided Instruction

Read the following information and answer the questions.

A bowling ball is heavy. It takes a lot of effort to roll it down the lane quickly, but once the bowling ball is moving, look out! A bowling ball is also hard to stop. This is because of inertia. Inertia is the tendency for a moving object to keep moving and for an object at rest to remain at rest. Mass affects inertia. The greater an object’s mass, the more inertia it has, so a bowling ball has more inertia than a baseball.

Bowling pins have inertia, too. The pins do not stay still when the ball hits them. Having inertia does not mean the pins will always be still. Having inertia means that the ball must exert a force on the pins to make them move. A force is a push or a pull. A force can push or pull an object to change its position and motion. For example, if you kick a ball at rest—the force—you will change the position of the ball and put it into motion. The amount of the change in motion is related to the amount of the force in your kick.

You can use a spring scale to measure force. Pulling on a spring scale attached to an object can measure how much force is needed to move the object.

5pounds

1pound

Figure A

Words to Knowinertiaforcegravityfriction

S TEKS 5.6(D) Design a simple experimental investigation that tests the effect of force on an object.S TEKS 3.6(B) Demonstrate and observe how position and motion can be changed by pushing and pulling objects such as swings, balls,

and wagons.

What Makes an Object Move?Lesson9

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Gravity is the force of attraction between any two objects. Gravity is another force that can cause motion. The greater the mass of each object, the greater is the force of attraction. Earth’s gravity causes all objects to fall toward Earth. That is why a ball will roll down a ramp. The higher the ramp, the faster the ball will travel.

Friction is a force that occurs whenever two objects rub together. Friction opposes motion and can slow objects. For example, there is friction between the soles of your sneakers and the sidewalk. Friction keeps your shoes from slipping on the floor. Friction also causes wear. After a while, the tread on your sneakers will be gone because of friction. Friction slows down a moving car, but if there were no friction the car would not move. The wheels would spin in one spot.

1. What is inertia?

2. Why does a bowling ball have more inertia than a baseball?

3. What is force?

4. Which block in Figure A requires more force to move it?

5. What is gravity?

6. How does friction between your shoe and the sidewalk help you move forward?

Science • Level E Copying is illegal. Measuring Up to the Texas Essential Knowledge and Skills56

Lesson 9 What Makes an Object Move?


SAMPLE

Critical Thinking

Answer the following questions.

1. Why is a rolling bowling ball hard to stop?

2. Why is a bowling ball hard to pick up?

3. Students set up the experiment shown below. They demonstrated the same four books for the height of each ramp, identical ramps, and identical cars. Car B has extra weights on it. Car A rolled a total of 2 meters in 3 seconds before stopping. What might they have observed from their experiment? What hypothesis could this experiment be testing?

Car A

Car B


What Makes an Object Move? Lesson 9


SAMPLE

★ Practice

DIRECTIONS Read each question. Then circle the letter for the correct answer.

1 What causes an object to resist change in speed?

A Gravity

B Friction

C Inertia

D Force

2 What is needed to push or pull an object?

F Speed

G Gravity

H Inertia

J Force

3 The force of attraction between two objects is —

A gravity

B speed

C inertia

D force

4 Which force stops a car from moving?

F The force of speed

G The force of friction

H The force of gravity

J The force of motion

5 What happens if a moving car hits a parked car?

A The motion of both cars stays the same.

B The motion of the moving car increases.

C The motion of the parked car increases.

D The motion of the parked car stays the same.

6 Which statement about two objects that collide after moving toward each other is correct?

F Both objects change shape.

G Both objects remain the same.

H Both objects change only direction and speed.

J Both objects change energy, direction, speed, and motion.

6

Science • Level E Copying is illegal. Measuring Up to the Texas Essential Knowledge and Skills58

Lesson 9 What Makes an Object Move?


SAMPLE

1 What is necessary for an object to move?

A Inertia C Force

B Friction D Mass

2 Why does a race car have more energy than a soccer ball?

F Cars are always faster than balls.

G Slower moving objects have more energy.

H Faster moving objects have more energy.

J There is a driver in a race car.

3 Sarah races a ball down a hill. She pushes the ball down the hill and tries to race it to the bottom. Why does the ball win every time?

A The rolling ball has more energy than Sarah when she runs.

B The rolling ball has less energy than Sarah when she runs.

C The rolling ball has less speed than Sarah when she runs.

D The rolling ball has the same amount of energy as Sarah.

4 Which would be the best example to observe an object’s force and motion?

F A parked car

G A person sitting in a car

H A car driving down the street

J A parking lot full of parked cars

5 A rolling soccer ball hits a soccer ball sitting on the ground and transfers energy. What happens to the motion of each ball?

A Both balls come to a stop.

B Both balls are in motion.

C The rolling soccer ball stops but the one it hits goes into motion.

D The ball at rests hits the rolling ball and brings it to a stop.

6 Which statement is true?

F When objects collide, their amount of energy and motion become the same.

G When objects collide, the one causing the collision always comes to a stop.

H When objects collide, both objects come to a stop.

J When objects collide, their amount of energy and motion change.

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★ Assessment

DIRECTIONS Read each question. Then circle the letter for the correct answer.


What Makes an Object Move? Lesson 9


SAMPLE

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